If you want something to do double duty for wildlife and to keep people away, there are a few options.
Anything from the thistle family is beloved by insects. This includes edibles like globe artichoke and decorative plants like echinops and eryngium. All are tall and spiky so not likely to make people want to push through. Acanthus is another prickly customer that has tall spikes of flowers that bees like.
If you put some trellis up or even just posts and wire, you could grow pyracantha or dog rose - both have thorns. After flowering, the hips of dog rose are very decorative and pyracantha has berries that the birds like to eat.
Once you have the barrier plants in there are lots of other choices. Open daisy type flowers attract a lot of insects so Japanese anemones, leucanthemum and erigeron are worth looking at. Herbs also work well especially rosemary, lavender, marjoram and thyme. You can grow annual stuff from seed like calendula, poppies and borage that would fill gaps. Add some spring bulbs and you extend the nectar season by quite a lot.