I just had my aquarium built with the overflow (which I keep covered) low enough that the distance from the top of the water to the top of the tank is 5 inches. So far, nothing has jumped.
It is essentially the same as a topless canopy, but the sides are made out of glass. It also doesn't splash when I use the magnet cleaners and the magnets are stored in the back corner, above the water level, which keeps them clear of algae and coraline algae. I like it.
Make the tank any size you want, but figure the gallons by how high the water is, not by how high the sides are.