My googling finds results that are all over the map - they are great, they are terrible, you do/don't get ricochets and bouncebacks, they do/don't catch fire, etc. Most comments don't specify details - are the tires empty or filled with dirt, etc. Some suggest it matters whether they are steel belted. The predominant opinion is that they work great, but I trust opinions on PF more than other random fora, and would love to hear from people with experience with them.
The situation: we have rural land. Stopping bullets isn't the problem; the target is at the base of a 300 ft ridge. The nearest neighbor is over a mile away, etc. But the soil is rocky, and this is wildfire country. When it isn't fire season, no problem, but in a dry August I reeeaaallly don't want to be starting wildfires. The predominant use would be rimfire, but occasional centerfire would be nice.
As a complicating factor, bringing in a dump truck load of sand isn't practical; it's a gnarly 4WD road. Even the materials I can bring via pickup have to be backpacked 400 yds.
I'm considering stacks of worn out tires; I can get similarly sized ones in quantity, enough for say a 5x5 foot barrier. I'd slightly stagger stacks so there is no chance of a pass through at the seam between stacks, and fill with the local rocky dirt. I'm assuming that hitting a rock inside a tire isn't a problem fire-wise.
Experience and advice welcomed.