Put in some big T-posts around the border, like 10 ft ones, one on each of the four corners. Once they're pounded in, string up some fairy lights around 9 ft off the ground and then another set around 6 ft off the ground. Assuming you have a ~4 ft fence with chicken wire for squirrels, this light configuration will keep them out--even if you don't keep the lights on overnight, since deer hate jumping into stuff they don't see ahead of time.

With this configuration, our garden has been deer-free in an area that has a ton of them. I see around 20 unique deer literally every day on my property, and I've never seen any of them in my garden, nor have I found any deer-eaten veggies.