Stay away from old tires:
Bullets do weird things when they hit tires. Normally you can tell what ricochets will do, not so with tires.
Our club used them, then noticed bullets were some how getting to power lines.
Also some rounds (22s mainly) will come back on you.
Burying tires doesn't help, they will flat to the top.
Dirt berms work the best. ties are OK but get expensive.
What ever you do stay away from old tires.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071