Back on the QDMA forum, this was a topic I spent A LOT of time researching. There were pages and pages worth of information - some were relevant to my situation, some were not. I think this is a thread that can help people like I was helped all those years ago.
In my experience, there are three ways to keep deer out of a food plot:
1) Milorganite
2) Plot Saver
3) Electric Fence
MILORGANITE
Milorganite is essentially recycled human waste from a sewage facility in Milwaukee. It comes as a small granule that is easy to spread in a 3pt spreader. It works because it stinks - deer do NOT like the smell and will typically stay away from it.
There are other types of Milorganite, so you don't have to buy just that name brand. A South Carolina sewage facility produces Poconite, and there is also a product that comes out of Virginia.
If you buy the commercial product at Lowes or a similar store, you will pay roughly $13 a 40 lb bag, which is a ripoff and cost prohibitive. If you have a local coop, talk to them about buying it in bulk. I was able to buy 1 ton of the Virginia product for $210 this year.
How to Apply
UGA did a study a few years ago and concluded that Milorganite works as a deer deterrent when applied at 250lb per acre TWICE. I apply it the first time at planting (if I expect the field to germinate quickly), and then the second application is exactly 2 weeks later. Even with heavy rain this is enough to keep deer off for a month.
I have had very good success with this method and will continue to do it if I can continue to buy the product in bulk. Each one of these sacks on my trailer is 1,000 lb of the Virginia version of Milorganite:

PLOTSAVER : http://www.messinas.com/products?categories=plot-saver
Plotsaver is a temporary fence that you put around a plot. It is a single ribbon placed 30" off the ground and then sprayed with a foul smelling rotten egg based solution. It is fairly simple to set up and take down, and you can use it year after year. I usually respray the rotten egg solution every 2 weeks on my small plots.
Plotsaver works...until one deer is brave enough to jump over it. That might take 2 weeks or it might take a month, but once one deer is over it the jig is up.
I've had good success with this product on one property and fair success on another with higher deer pressure. It's worth trying on a small plot to see if it works on your deer.
Electric Fence
This is the Holy Grail of Food Plot Protection, but I am NOT an expert on it and thus will wait for someone like dgallow to chime in if he is willing. My one trial at establishing an e-fence was not successful, and I haven't been brave enough to try again. I used a 6v solar charger made by Parmak and never could get the volts up high enough to keep the deer off.
However, many, many users on the QDMA forum had great success with an e-fence, and this was the consensus winner as far as food plot protection was concerned.
In my experience, there are three ways to keep deer out of a food plot:
1) Milorganite
2) Plot Saver
3) Electric Fence
MILORGANITE
Milorganite is essentially recycled human waste from a sewage facility in Milwaukee. It comes as a small granule that is easy to spread in a 3pt spreader. It works because it stinks - deer do NOT like the smell and will typically stay away from it.
There are other types of Milorganite, so you don't have to buy just that name brand. A South Carolina sewage facility produces Poconite, and there is also a product that comes out of Virginia.
If you buy the commercial product at Lowes or a similar store, you will pay roughly $13 a 40 lb bag, which is a ripoff and cost prohibitive. If you have a local coop, talk to them about buying it in bulk. I was able to buy 1 ton of the Virginia product for $210 this year.
How to Apply
UGA did a study a few years ago and concluded that Milorganite works as a deer deterrent when applied at 250lb per acre TWICE. I apply it the first time at planting (if I expect the field to germinate quickly), and then the second application is exactly 2 weeks later. Even with heavy rain this is enough to keep deer off for a month.
I have had very good success with this method and will continue to do it if I can continue to buy the product in bulk. Each one of these sacks on my trailer is 1,000 lb of the Virginia version of Milorganite:

PLOTSAVER : http://www.messinas.com/products?categories=plot-saver
Plotsaver is a temporary fence that you put around a plot. It is a single ribbon placed 30" off the ground and then sprayed with a foul smelling rotten egg based solution. It is fairly simple to set up and take down, and you can use it year after year. I usually respray the rotten egg solution every 2 weeks on my small plots.
Plotsaver works...until one deer is brave enough to jump over it. That might take 2 weeks or it might take a month, but once one deer is over it the jig is up.
I've had good success with this product on one property and fair success on another with higher deer pressure. It's worth trying on a small plot to see if it works on your deer.
Electric Fence
This is the Holy Grail of Food Plot Protection, but I am NOT an expert on it and thus will wait for someone like dgallow to chime in if he is willing. My one trial at establishing an e-fence was not successful, and I haven't been brave enough to try again. I used a 6v solar charger made by Parmak and never could get the volts up high enough to keep the deer off.
However, many, many users on the QDMA forum had great success with an e-fence, and this was the consensus winner as far as food plot protection was concerned.