Try using a figure-eight knot making a loop then retracing the knot. with the loose end. This knot has similar properties as the bowline except it has to fail twice before coming undone. It can hold 350 pounds with weaker rope than spectra, and I have trusted my life to it. (Note: I am not an Eagle Scout but am turning in my paper-work to become one next week).
Here is a link on how to tie it. The first section is the one i am describing, and the strongest.
http://www.chockstone.org/TechTips/F8Knots.htm