When I was a district fisheries biologist in Kansas, we used a lot of tire structures. Typically, we tried to make them as 3-dimensional as possible. For example, we would stand 6 tires upright, and use a thin steel cable to bind them together. Then we'd do a second row, and set them side by side. Then, we'd cable those two rows together. Then, we'd set a third row on top, and all of a sudden, you have 60 inches of height, rather than 30. All tires were punched (holes), as indicated by others, to let out gas bubbles.
We also made a big floating tire breakwater to cut down on wave erosion along an exposed shoreline. Again, a big (can't remember, must have been 3/4 or 1 inch steel cable that we got from miltary surplus) was used to hold the tires in place. These tires were not punched, as we wanted them to float. The anchors were big steel pipes that were anchored into deep concrete auger holes.
My primary point here is the steel cables to hold them together. There is nothing (in my opinion, I guess) that looks worse than tires floating up along your shoreline. Looks like trash to me. Don't tie the tires together with nylon rope or nylon straps. Eventually, they'll break, and you'll have a clean-up chore.
Dave
