You can keep them out for awhile. I put a non-electric fence around my soybeans, then sprayed it with deer away. That kept the deer out until the beans were big enough to handle grazing, but they eventually ignore any 1 repellent after awhile. Switching products regularly may help.

Here is a warning though. This guy showed up 10 minutes after I sprayed deer repellent, and was eyeballing that fence. He ignored me pounding fence posts, the parked car, and us talking to each other. These things are more destructive than 20 deer.