Personally, I don't think that's a silly question at all. I don't know that I'd necessarily want it "removable" because if it's not so tight that you can remove it, you risk the snake finding a way behind it and possibly getting trapped. Also, removing a piece of foam board like that would be difficult as it can get crumbly. Velcro or an adhesive spray would make it less permanent, but I think for general cleaning, you'd want to just be able to wipe it down, which is why I suggested polyurethane. That way you could spray your chlorhex or bleach or whatever you used for cleaning on it and it wouldn't harm it.
Again, this is just my 2 cents. My viv background is completely siliconed to the back because it was previously used under water. There's no way I could get that thing out without a ton of work, and I'd definitely ruin the piece in the process.