You're building an in-ground disappearing fountain. If you do an internet search, you'll find lots of ideas and kits.
Instead of wire mesh, think about a round plastic bucket, 8-10" deep, inverted in your container. Much more stable than trying to balance or suspend a piece of mesh and easily covered with rocks. You can place a small pump on top of the bucket (actually the bucket bottom) or put a larger pump in the bottom of the container and cut a hole in the bucket for a fountain pipe.
The other reason to use the bucket arrangement is to protect birds and small animals. A critter trying to drink or wash in the fountain can get caught in wire or plastic mesh (even covered with rocks) or can tip a suspended piece of mesh and be trapped underneath.
When you place the rocks, build up one side level with the ground so anything that crawls in can get out. Also leave a bare spot where you can check the water level. Wind and evaporation will empty your container every few weeks and running a pump without water will burn it up.
