Holster mods

[Animalguy]

I'm looking for something to put on the backside of holsters to create some grip.
I've worn both leather backed and straight kydex holsters and both can feel like they have a little too much movement on my undershirt.

I haven't read about a go-to way to do this. I'm imagining a couple of beads of some dry rubbery adhesive, or neoprene backing.
Any ideas?

 

[BLIP]

Try a rubber band. Don't glue it loop it.

 

[bulletpaluza]

Tighten your belt. Mine never move and they are just kydex.