Most fencing experts recommend setting fence posts in concrete at least two feet into the ground. Our vinyl fence installation experts at Future Outdoors always set vinyl and wood fence posts 3 feet into the ground for our 6-foot and taller fences for extra stability and strength. The mistake most homeowners make, though, is thinking that a 3-foot-deep hole equates to setting a post 3 feet deep.
The best way to ensure your holes are deep enough is to rent an auger with a 10″ auger bit and dig to the 3-foot mark. You will need to run a string line for the top of the post and the horizontal post placement.