Best way to make moss stick to enclosure background?

I’m trying to make a paludarium and am using great stuff pond and stone expanding foam for the background. I’d like to attach moss to this foam with a kind of moss tack, but am unsure about the best way to do this. Does anyone have any advice?

I've heard of people using air plant fixative spray, but it is silicone based and would require you to roughen-up the surface probably

Would be interested to know how/if you managed to do it

In the aquarium hobby we do this fairly easy by chopping up moss or even sticking it into a blender. Add a little bit of spagnum moss (this is optional,some say the moss will retain more water due to the spagnum) and add some water so you end up with a smearable substance. Note that some add buttermilk instead of water as it's said to give extra nutrients to the moss. However some also noted that this might increase the risk of mold. Personally I'd just stick with the water as I've had good results with that.
Now that you've chopped up/blended your precious moss with the spagnum and water you're ready to smear it onto any hardscape you want. Rocks, wood, background etc. The moss will attach and needs to be kept moist and plenty of light. Not too wet as you might spray off the moss before it had a chance to attach. Give it a few weeks time and you'll have a lush background of moss that has grown in naturally without the use of any silicone or superglue.

Cyanoacrylate super glue

If you're attaching bunches of moss, particularly if it has soil still on the roots, super glue (cyanoacrylate) is the way to go. It's plant safe and critter safe once it dries.
check out some of the more prolific youtube paludarium makers, and you'll see them all using it extensively.
if you have rocks and crevices, you can also just 'stuff' it in there, and if you keep it moist, it will root on it's own.
I generally do a mix of both...

The blender method works as well, but it takes a while to grow in...