Fishing line. String it up all around your plot. I like to tie the end of the line to a tree/sapling about 2 feet about the ground, and walk around each one of my plots tying it to different spots. I will then go ahead and make a bunch of passes around a different hiehgs making sure that if a deer were to walk up unsuspectingly, it's gonna get all fucked up and tangled in the mess scaring it away.
I spray beer cans black and leave 4 of them open around the perimeter of the plot, this keeps slugs bugs and deer away. Also, Coyote pee pee or Fox pee pee work really good as well. Depending on how often you go to your plot and how many plots you have, will determine whether you should bring out a weapon of some sort. Deer will only not go to that area for a couple of days after spooking them out. As an avid hunter i know this. However, deer are pretty dumb. I have killed a deer from a treestand, gutted the deer and left the gutpile there. I decided to be lazy and try sitting in the same stand the following morning, and shot a nice 8 point where i killed a doe the following night. So the smell of a dead deer is not a deterrant. Also, humans do not have a hormonal scent in their pee, making it not very effective at detering deer. I have pissed on my tree that i was standing in and have had deer walk right in. Fox Urine is the way to go, or if you can find it, bear pee.