The sand and epoxy works great for wooden holds, too. Don't make mixture too thick, as it gets hard to apply.
Do all your prep in advance, marking where you want the texture. Have some extra sand handy, and pat it onto the holds while the epoxy is still wet, then wire brush off excess later. Use goves, as it is toxic.
Also, for wall application, use less sand than for holds in the mix, as it tends to clump more on a roller.