I have a 3 strand electric fence surrounding my main growing area. You can pick up a relatively inexpensive fence charger, aluminum wire and fiberglass poles at Tractor Supply or your local hardware store. It's easy to make a small gate for access if you also purchase an insulated handle to unhook the top strand.
The most important thing you can do when installing it is to make sure you use a good ground rod, driven into the soil
at least 4 feet. If the fence isn't grounded well, the electric shock will be weak, thereby ineffective. Look for a high joule rating on the fence charger before you buy it, too.
Skunks, opossums, deer, raccoons, woodchucks, rabbits, chipmunks, squirrels and weasels are abundant here and all have been known to dine on tomatoes.