You can find these magnets in the magnet section of a hardware store or a craft store.  They are typically sold in packs of 6 or 8. If you cannot find any, get a set of magnetic jewelry clasps from the beading section of a craft store instead. You can use smaller magnets too, but don't use larger ones. Do not use the  standard "black" magnets either; they are not strong enough.
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One-sentence summary -- Get a pair of 1⁄4 in (6.4 mm) silver neodymium magnets.

Article: There are many different ways to set up a pond with a waterfall system. The easiest way to do it is to stack rocks to create a spillway on the edge of your pond. You could also dig out the soil to create a lower pond and an upper pond. Connect them by having the water spill from the upper pond to the lower one or by building a sloping stream between them. If you already have a pond in your yard, pile up soil and rocks to create a shelf for water to spill from. This is the easiest way to get a waterfall since you get to avoid a lot of extra digging. The water falls from the spillway to the pond, then enters a pump system you install to bring it back to the top. To create a stream, you need to first dig out a pair of ponds or basins. Then, dig out the stream to go from the higher basin to the lower one. The stream has to be sloped to move water downhill, so working on a natural incline in your yard reduces the amount of digging you have to do.  With a stream, you have the option to build many small waterfalls. Arrange the rocks in the stream to create shelves for the water to spill from. Stream waterfalls are long compared to pond waterfalls and require a stronger pump and a longer hose. For example, streams are generally at least 3 ft (0.91 m) long, so you need to commit more space in your yard to set it up. If you have limited space or a yard that isn’t easy to build on, you still have a way to get a good pond. Stack strong building material like limestone boulders to build a basin that catches the water. Then, stack more of the material on one end of the basin to create an area for the water to fall from.  You could build a basin out of resistant materials like cinder blocks or bricks. Above-ground waterfalls come in many styles, so let your creativity loose when designing yours. To hold the pond together, spread a waterproof expanding foam around every rock. The building material has to be strong and well-sealed to hold the water in place. Most pond and stream waterfalls involve a little bit of digging. For this type of waterfall, you basically dig a hole in the ground, then make a vertical stack of rocks on one end. Place a water hose in the rocks to spill water down and into the basin. This is called a pondless basin, and the water gets circulated continuously through a strong pump. This type of waterfall is similar to any basic pond waterfall. If you don’t already have a pond or a water basin, you could dig a new one before building your waterfall. The average size of a pond with a built-in waterfall is 10 ft × 15 ft (3.0 m × 4.6 m). If you’re planning on making a stream or a pondless basin, do some math to estimate the minimum size you need. Generally, the basin has to hold about 2.5 times the amount of water circulating through the waterfall.  To figure out how much water is in motion through your waterfall, measure the waterfall’s length, width, and depth in feet. The formula is length x width x (depth x 0.25) x 7.48. The 0.25 is the thickness of the water and the 7.48 is the number of gallons in a cubic foot.  Then, multiply the amount of water in motion by 2.5 to figure out how many total gallons of water you need. For example, if your waterfall is 10 x 3 x 0.5 ft in size:  10 ft x 3 ft x (0.25 x 0.5 ft) x 7.48 gal/cubic ft = 28.05 gallons of water in motion. Then, 28.76 gallons x 2.5 = 70 gallons of water needed in the pond. Remember to do the same for the upper pond or basin if you plan on building one. Keep it roughly the same size to ensure water moves through the waterfall at a steady rate. Put your waterfall in a spot where it can be enjoyed from different angles, both inside and outside your home. The best spot for a pond is usually near a deck, patio, or window on your home. These areas also tend to be accessible to water spigots and electrical outlets you may need to power your waterfall. Also, since waterfalls are all about water falling from a higher area to a lower one, build on a natural incline to reduce the amount of digging you have to do.  Any ponds connected to the waterfall require about 6 hours of direct sunlight if you’re keeping any plants or fish. For example, place the pond close to a water spigot so you can easily fill it with a hose. Also, the pond’s lower basin needs to be within range of an electrical outlet to operate the pump. However, connect the pump with an extension cord to prevent water from splashing onto the outlet. Gravel is very important for covering and pinning down the pond’s liner, so purchase plenty of rounded gravel or river rocks. You also need plenty of boulders and flat rocks to line the stream. These larger stones are great for decorating the pond and covering some of its construction components. Flat limestone rocks are great for creating waterfall spillways, while larger boulders are useful for framing the pond.  Most home and garden centers have limited supplies of pond-building material. For a bigger selection, search for quarries and stone suppliers in your area. To figure out how many boulders you need, multiply your waterway’s length and width, then divide it by 65 tons per foot. This gives you an estimate in tons, but keep in mind that rocks come in different sizes. For instance, if your waterfall is 10 ft x 3 ft in size, you need about 0.46 tons of rocks for that area. Estimate the amount of gravel you need by taking the amount of boulders in tons you need, then dividing by 0.45. The gravel layer generally has to be about 3 in (7.6 cm) deep. For example, if your waterfall is 10 ft x 3 ft, you need approximately 1 ton of gravel to fill it.
Question: What is a summary of what this article is about?
Create a waterfall with a pond if you plan on keeping plants or fish. Build a stream if you prefer a long, gentle waterfall. Make an above-ground waterfall if you can’t dig out your yard. Design a below-ground waterfall if you are able to dig out your yard. Choose the size of your waterfall and basin before beginning construction. Select a visible location about 20 ft (6.1 m) from your home. Order gravel and stones to use to build your stream.