I use 3' sections of rebar, unbent that I got for Home Despot. You'll need a sledgehammer to get them in and you'll need a good pair of Vice-Grips to get them out. A few twists of a Vice-Grips and the rebar will come loose. Don't bother trying to put water down the side of the rebar, that does not work at all.
On the dome we use 4' sections of rebar bent in a semi-circle. We pound those in with the Sledgehammer and remove them with the sledgehammer (we broke our sledge removing them this year). The dome rebar is MUCH more difficult to remove than my rebar tent stakes.
The major problem with the unbent rebar is that you have a 6" section sticking straight up for someone to get impaled on. To remedy this I put Tennis Balls over the exposed rebar ends. Our neighbors had a better cap system that was actually made for covering exposed rebar but they aren't really necessary IMHO.
Camp FuckIt + MT - 7:15 & D (maybe)