 Squash bugs are very mobile. They fly. You may not have them on your property, but if the neighbors do, they'll find you. Now you can plant squash bug-resistant plants and cultivars like any kind of butternut is more resistant to them. And that's great. But if you also plant out, say, a highly susceptible zucchini, attract them, then manage to kill them on the zucchini, however it is you do it, then you might be on to something.