Tape works, rubber bands work, some people rig up something to hold a pencil straight out and then turn the gourd next to it to create a line. Always pencil in a guide, no matter what you choose, freehanding this, unless you're incredibly good, usually doesn't work. I've also thought (but haven't tried yet) that one of those laser pointers used in carpentry would be a great way to define a line, they are supposed to go around corners! :)

Thanks, Caseyst. Will try the tape and see how it comes out. I do know from reading that I need to cut at a slant in order for the lid to stay on. Will let you know how it goes.