In smaller areas, such as a family vegetable garden, deer here seldom jump a 6' fence unless it is shortened by snow. If there is drought and food is scarce, all bets are off, however.
The last 2 times deer began jumping my 6' garden fence I simply stuck some rebar stakes into the ground every 10' or so about 2' outside my garden fence. I then stretched 2 strands of mono filament heavy, deep-sea fishing line to the rebar, one about 20" off the ground and the other at about 3'. Because they like to sidle up to a fence before jumping it, this has been completely affective in turning them away.
I would bet that this mono-filament augmentation could be effectively used in different ways to deter fence jumping in larger protected areas. I've also used a couple strands to extend the height of a sturdy fence.
Another trick used by fencers around here to get around codes limiting height is to have a perpendicular lip that is like a 2' horizontal fence extending inward from the top of a 6' fence. It seems to work well, probably similarly to a slanted fence.
[NAFEX] stopping deer from jumping fence,
Alan Haigh, 02/28/2009