really dumb question (Tank background)

[m1a1fixer]

I don't want to paint the back of my tank right now, so I'm going with a background. What is the best way to attach that to the tank? I used tape on my FW, but it tends to eventually let loose and peel back. I did spill some water between the background and the tank once and the background seemed to stick to the tank for a day or two. Does that work in the long run if you do the entire background or was it a fluke? Thanks for any assistance you can give with this basic question.