The tire will slow 'em down but not necessarily stop everything.

I assume you had at least somewhat of an earthen backstop.... a bit of a small hill at least. If not, you were not shooting in a good spot at all.
But assuming you had a bit of an earth backstop and the bullets were STILL ricocheting ,, then loosening up the earth behind the target with a shovel and a 3/4 " pice of plywood would probably be enough to slow everything down. FOR .22 ONLY, we used to take a couple pieces of 3/4 " ply about 3' X 3', and screw them together ... we then screwed a couple "legs" (2 x 4's) into the top along each side so they could pivot. We'd stick the legs in the ground and have the plywood top be angled towards the back of the target, the bottom away (kinda like how bullet traps are set up) only this wood didn't trap anything, only gave the bullets something substantial to tear into, slowing them way down (sometimes stopping shorts). Then, when slowed bullets passed through they were then met by the newly churned up earth that we would loosen directly behind the "trap". We'd set up the targets directly in front of the Trap and loosened earth. Again, this should always be done where you have a good earthen rise or backstop.

Since that time we've found a county gravel/sand pit that works great .. and no one bothers us at all.. No more lugging around the plywood!