Unfortunately, you'll probably have to keep your cat indoors to avoid fights.
One way to give your cat the outdoor experience without the dangers of fights is to build an aviary-type structure, so your cat can sit outside, but in a large, wire-enclosed cage. If you have a convenient spot, you can build it up against the house so your cat can go in and out via a window or cat door. A screened porch is also a viable alternative, although you might need chicken wire over the screens to prevent the cat from pushing the screening out in a corner and escaping.
Once your own cat is contained, there are motion-activated sprinklers that might discourage the neighbors' cats from entering your yard.
