I earlier posted ideas on IED detection. One of the comments brought up how a team had worked out a defense against RPGS -- basically a radar unit to detect incoming ones, then fire a shotgun blast at them, that disabled or detonated them. Check out the comment for details.
Yup, detonation would probably be halfway frequent: from what I understand, the fuze is a piezoelectric crystal that generates an electrical pulse. Anything that hits that fuze with sufficient force would detonate the round, even if the projectile itself is hardly slowed.
The other quirk at least the earlier models have is that the electrical pulse travels thru two metal layers, I believe the outer casing and an inner one. Anything that dents the casing shorts it out. Ordinary chain link fencing worked well in Vietnam, for a stationary vehicle. I wonder if that couldn't be upgraded. Say overlapping metal or cable circles, of almost the same diameter as the RPG, hanging loose so that they pivot upward when struck. Perhaps a few teeth on the inside of the ring at the lower end. A round that hits is unlikely to hit on the fuse, and thus may not detonate. The casing will be dented pretty badly as it spins. If it does go, with any luck it will be directed upward. The problem may be strength, as those things accelerate to (if I remember correctly) around 800-900 fps.