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.

A tip I got from an orchard owner is to use human hair clippings. They just got them from a barber shop and stuffed them in cans attached to the trees. Aparently the smell helps keep the deer away.

Also cat or dog urine can help keep them away. If you have an indoor cat then you can "mark" the area with used cat litter and that should keep them out. You can also just buy straight up bobcat urine online for that purpose. I'm not sure if it works any better than regular cat or dog pee, but it is available.