Need some creative ideas for 3D background installation

[Sylerwin]

Hey folks, so I'm in the process of building 3D aquarium backgrounds. I have a small one for a 5.5 gallon tank that I've been using as practice. ALL of the tutorials that I have read so far say that it needs to be siliconed in place to the back of the tank to prevent it from floating up (it's made out of foam). HOWEVER, I'm trying to make it so that it can easily be moved for cleaning purposes, and for any repairs that may need to be made to the sandfall (underwater waterfall) I am also installing.
To get an idea of how much weight/strength will be required, I tried weighing down my little 5.5 gallon practice wall. It took 1 slate tile, a vase filled with water and marbles, a river rock, and a huge chunk of petrified wood. Now, the one for my main tank, my axolotl tank, is a 40 gallon. So basically, whatever is holding down the 5.5 gallon tank, needs to be about 5x stronger than the little one, as there's just that much more foam. I've tried magnets, but the ones I got weren't nearly strong enough. Any ideas would be greatly appreciated!!!

 

[ZombieAxolotl]

My first thought would be to make the background so that it had a kind of pocket at the bottom you could fill with sand to weight it. but the foam would need to be able to esentially hold that much weight or it would break when you lifted it.

i've also siliconed a background to a large piece of slate to hold it down. but it sounds like yours would be to "floaty" for even a large piece of slate.

Can you incorporate a weighted object into the background piece via some silicone?