I posted this over on G+, but I decided it was worth repeating here.
Keeping the Flock On
One issue I've had with flocking/basing minis, is that the gravel, grass, etc. falls off over time. It is glue down but that's not sufficient when it comes to surface friction and just sheer aging.
So I have a two-part method to flocking bases for minis.
Step One: Flock
Coat the base with white glue (Elmer's, if possible, the cheap stuff is close but is often too watery, but see below). Dip the glue-coated base in the appropriate basing material. I may glue only sections, if I want a mixed base, or glue the whole thing and just stick on extra bits with additional glue. This provides a pretty solid base of adhesive for the flocking to stick to.
Step Two: Seal
Once the basing in Step One is dry, I mix a 50/50 water/glue mix and coat the flocking down with that. Basically I submerge the base in the 50/50 water/glue mix and then, once it has soaked through (it only takes 30 seconds or so), I take it out and wiped off the excess.
When that dries, it still looks the same but then has a nice hard shell holding it on. It's messy to do, but effective. The watery mix means the glue coats everything and gets into the cracks and gaps between gravel and sand and "grass" alike.
You can do the same thing with CA glue, at least for step one, but I find you'll need to repeat step 2 an extra time or two if you do so. CA glue is strong but lacks some side-to-side holding strength and will lose basing material sooner than flock embedded, basically, in a thin but continuous layer of white glue.
Give that a try next time you base with grass, gravel, or sand, and let me know how it comes out. It's held up pretty well for me when I have take the time to do it right.