I HATE those vine borers. I put up a lattice on my front porch so I could
grow miniature pumpkins, small squash and gourds. Since the plants grow up
into the air, they are very vulerable to the vine borers at the base.
I have read that it can help to wrap the first few feet in nylons
(pantihose), but I have not tried that myself.
In the next year or two, some genetically engineered vine crops are
supposed to come out that have the genetic capability to automatically kill
the larvae when they start to eat.
Another possibility to use ONLY if nobody is going to make pies, or eat
any of the pumpkins: you could use something like di-syston systemic
insecticide. This is a powder you apply at the base of plants, usually
ornamentals. The plant takes the insecticide up into its sap, and any
insect that feeds on the plant dies. Trouble is, if you try to feed on the
plant, you could get sick or die, too. This would work out fine for you if
you are just wanting jack-o-lanterns and pumpkins for fall decorations.
However, you would have to make absolutely certain that nobody was going to
try to use any of them for food purposes.