for defending my homeworld, i put a force field over the wormhole on the other side, after i take the planet.
ok, crazy idea. if you have a lot of tractor beam immune ships coming through, and they tend to always go in the same direction, what if you put up a pair of level 1 force fields? have them set up in the right position, so that incoming ships would have to go a longer path, giving your turrets more time to shoot them, and your ships will have more time to get there if necessary. then again, a mine field with a mine layer would probably work better.
basically it would be set up so that there is a little crevice for the wormhole, and they can't go straight for their target, instead they have to go all the way around the two force fields.