8' feet will stop MOST deer, but 10 is far more effective. When pressured, I have seen mature whitetails clear an 8' foot fence pretty easily. However, most deer will not voluntarily jump it. Typically, they have to be pushed, startled, or driven over it. Amazingly though, I have seen an Axis clear a 10 foot wall though. It was not pretty, but it jumped, got hung on the top then slid over. This was all standing and jumping "flat footed" (or flat hooved!). Any way, back to the point an 8' foot fence should do the trick. An easy way to get a away with "stretching" the 8' foot fence is to add 2-3 strands of barbwire. It will stop them.