Help tweaking my Rhyperior

I went for a Rock Polish set, but since is mostly bulking hits and STABing everything is not worth it to try to outspeed certain mons. I wanted to go with sneaky pebbles but no tutor or anything legit on XY for it.

Until Stealth Rocks is legally available I am looking for an Assault Vest set but dunno if the invest on Sp. Def will make him close as bulk it is physical. Also undecided if go for Poison Jab against Fairies and Grass or go for buffs with Power-Up Punch.