The easiest and most practical way is to place the heater behind décor so that it's not visible. You can lay heaters horizontally on the bottom level of the tank. There are some heaters you can place in-line with the canister filter so it's not even in the tank, and that's probably your best bet if you don't want the filter and heater to show. You can also work a sump combination and place the heater in the sump.
David