I know Austin Energy would require a 7' fence, as I did some school projects for them in the past. I also did some similar projects for the TX State Energy Conservation Office that did not require a fence. These were all pole mounts, so any exposed wiring was technically not readily accessible by virtue of the height of the arrays.
A ground-mount is inherently more difficult to secure. Even if you can block access to the single conductor wiring, how do prevent kids from climbing on the arrays? A 7' fence might be the only way to really secure things.
(By the time you factor in the fencing costs, carports or shade structures might be more cost effective - and useful.)