Keeping deer off of a food source depends on a lot of factors including the availability of other quality foods and perceived risk. They also habituate quickly so once they get in once, it is harder to stop them a second time. Yes, they are limbo artists. I doubt barbed wire without juice would do any better.
There are lots of “light” techniques from sprays to fishing line to miloganite that make accessing your food source less attractive to deer. The level of effectiveness really depends on the factors I first listed.
A high fence (10’) is effective, a Gallagher-Style e-fence is effective a 5’ solid fence that deer can’t see through is effective. The right dog can be effective. Everything else may or may not be effective depending on the other factors.
Just to give you a little example. Before I used the Gallagher-Style fence, I tried one of the ribbon systems that uses an olfactory deterrent on the ribbon. I figured I’d try the cheap route since I could re-uses the step-in posts with a Gallagher-style fence if this attempt failed. I applied the solution to the tape weekly at heavy doses. Again I only protected a small section of the soybeans I had planted.
After a few weeks, if you took a picture you would swear the system worked great! Beans outside the fence were browsed heavily and a fraction of the size of the beans inside the fence. After the deer pretty much polished off all the beans outside the ribbon, they got bolder and started breaking inside the ribbon and eating beans. Once they learned that the olfactory deterrent did not represent real danger, they completely ignored it. Before long you could not tell any different between inside and outside the ribbon.
This is just an example of how some low levels of protection can work very well for some folks in some situations and be completely ineffective for others under different conditions. As I said, in some areas folks even needed a 3rd higher line on the inside of the Gallagher-style fence to prevent deer jumping the fence. As the example someone gave earlier, it is even possible for deer to jump a 10’ fence under some conditions.