I simply use a wood glue like tite bond. Pour it on and add the rocks or gravel or sand. Dries clear and then i will cover it with a high gloss laquer. Looks wet and easy to clean the dust off the mount down the road.
Sorta similar. I just lay a decent layer of Elmer's glue and and the rocks. I usually do artificial though, but I'm sure it would work on pea gravel as well. Then after dry, a litght gloss to the rocks. Although I do find Rhasputin's method worth trying. Kills two birds with one stone so to speak...