Best advice is the Mod-Podge. When you get it though, make sure you read the label to get the right one for the project you are creating. There are two kinds and they are for different materials. Both come either as matte or gloss. Good luck. I use it for coating my completed puzzles so they are ready for framing.

Mod-Podge, not only will it hold in place but it also does the job as a sealer, a water proof sealer and after it dries you are done, done, done. I can't live without it.  If you want a little more polish or just assure yourself more spray with gloss or matt acrylic spray available at Joann also (mod podge too).  Easy as pie. Hlope this helps

epoxy

What about a thin layer of polyurethane?