Mark the location of where the post holes will be dug. String a line between two stakes for each face of the fence. This identifies exactly where the line of the new fence will be constructed. Using a tape measure and marking paint, measure and spray a mark on the ground where each post hole will be dug. Use the required spacing measurements for the fence. For example, standard spacing between posts for a 6 -foot-tall wood fence is 7 feet 9 inches.
Attempt to dig at each mark using post hole diggers or an auger. Some holes will not be able to be dug out due to roots. These post holes will need to be moved along the fence line.
Move the problem post hole locations along the fence line. Try digging along the fence a foot on either side to discover a place where the roots are not a problem when digging. If these new locations don't work, continue down the fence line on either side until a suitable post hole can be dug. This will change the length of some fence panels. Some panels will ultimately end up being very short or very long. Compensate these size differences with the appropriate-sized fencing materials.
Complete the hole digging process and set the posts. Finish building the fence as normal, but compensate the newly sized panels with the appropriate-sized materials.