when they bite the entire top off - well that's how it works around here anyway...

Some just don't develop.
They grow pretty much on their own, actually.
The birds appreciate the dried heads which I cut after the seeds have set. I hang them upside down from tree branches, and let the seed eaters go to it.

http://www.democraticunderground.com/1018141509

a nice small one that has multiple heads. one big one, then smaller ones down the stem after. not so big they fall over, and not quite as irresistible to squirrels as the giant ones.
this is my second year growing them. love them.