five -- evenly distributed around the dome. I use 2' rebar (5/8" diameter). I don't bend it. I just pound it in straight. I position each on the inside of the dome, right over a vertex, at an angle so the end points outside the dome. Then I cover the top with a tennis ball that has a hole poked into it (or one of those nice rebar toppers that look like an orange mushroom -- you can buy them where they sell rebar).

I also cut short lengths of those pool noodles and slide them over the rebar. The pool noodles are hollow tubes of plastic foam people use in swimming pools. You can get them at lots of places in the summer -- wherever they have pool toys, or Toys R Us, etc. I bring a couple with me to BM and cut them on-site to the needed length. These protect toes that my kick rebar.

Rebar injuries are unfortunately very common at Burning Man.