I would probably do some of mine differently were I doing it over. I found PBF after I already had my structure for the most part done and the pond was filling up. So I did not gain the benefit of what I have since learned here on the forum.
One pile I just stacked them flat in a circle, then an overlapping circle inside that, then another on top of that forming a tee-pee shape. I drilled holes in the sidewalls and stuffed rocks in and around the tire beads to hold them open and as ballast. I would not particularly recommend doing it that way. There are a lot more effective ways of doing it and the structure archives describe some of the methods. Most of my structure was out of concrete foundation pieces, cedar trees, and inverted stumps. So the tires were kind of an afterthought and I did not put the effort into them to gain best effect, in my opinion.
The tractor tire and semi tires I leaned and stuffed them in and around my concrete foundation beams (concrete stacked up Lincoln log style), drilled holes in them, and put some rocks inside to keep them from floating.
I did have one derelict tire float to the bank which I had to re-position and re-sink after the pond filled, so it is important to get enough holes that gas does not accumulate in the inside of the tire and float them. Even if you get the air out initially and the tire sinks, pond gasses formed from muck can still accumulate in cavities and float them later. So the holes are needed so there is an escape route for gas buildup.
Since I did my structure, I have seen lots better use of tires than what I did. Check out the archives although unless you have a browser plug in a lot of the pictures have been lost access to. I think some browsers have a work around so those pictures can be viewed.
structure, cover, etc archives here Edit: I see a lot of the old links are not working, including the one on tires. Sorry about that.
