Range ground marker

I have a small firing range setup and I got tired of bringing out a measuring tape and spray paint to mark new lines every couple of weeks. I wanted something that stuck in the ground well enough I could mow the grass without it coming out and strong enough that it would survive being ran over by a tractor. I printed them with 6 walls and used PETG. So far they survived a 4ton tractor. If I eventually break one I might try printing it with TPU.