I hate to be a downer but...
Unfortunately the pumpkins get nasty with time, no one comes back to pick them up and they sit there and rot after Halloween. The PH can be cited for littering and some places, like Westwater, have been cracking down on the practice because they've become such a problem. Someone will have to carry that stuff out and a pumpkin here and a pumpkin there will soon be enough pumpkins to fill up a work party boat or two that could be hauling out old tires and junk.
If you think leaving a pumpkin on some prominent rock will look really cool, ask yourself how cool it'll look sitting there on Nov. 1, or Nov. 15, or Nov. 30.
Maybe the rule of thumb should be, "only leave pumpkins if you're definitely going to come back the week after Halloween, rain or snow, and pick it up and haul it out. And all the others."
If you pack it in, please pack it out.
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse