I'v had trial & error trying to find a glue that basing materials will stick with. I.E When basing my lizardmen for this march paint plegde I resotred to super gule, even that didn't go as planned. Any ideas would be helpful!
For sand and small rocks, I use white school glue, then let it dry, then I put a 70/30 mix of White Glue/Water on top to seal it. After that you can super glue down any static grass or tall grass or whatever. You can check my plog in my signature below for the results. They are nothing spectacular, but it works.