To prevent overfilling the dead space or drainage layer, you need to have a way to remove the excess water. The simplest construction is to use a clear 1 in. diameter plastic tube similar to an under gravel filter lift tube. You install that vertically so it reaches the tank bottom. Insert tube into a piece of foam (to prevent it from clogging) and then it goes into dead space or your drainage layer goes on top. When you see the water level rising, can insert and aquarium air hose or similar into the tube and using suction/gravity, remove the excess water.

The other way requires drilling a hole (use glass shop if do not know how) at bottom glass pane (if not tempered) or lower area of a side pane. Then you install an aquarium bulkhead with valve and tubing so you can drain water as it level rises. If you search YouTube for "installing aquarium bulkhead" should find a few videos on procedure.

What are you using for an enclosure? Aquariums should not leak and even turtle or reptile enclosures should be able to hold a few inches of water. Good luck !