Yeah the e-collar is your best bet. When my little Kota got spayed a few weeks ago she pulled all of her stitches out even though the vet gave us some bitter spray to put on her tummy. We kept her seperated from our other cat with the e-collar on so that she wouldnt lick her incision, then took it off when it closed on its own.
They are pretty cheap, like Kitty's mom said you can ask your vet for one or get one at a pet store. Some come with snaps, some tie on with a ribbon...Kota had the ribbon one and got it off once in a while, you just have to keep an eye on them, and make sure they get a break from it when they need to eat, etc.