Extra charges are a source of frustration for everyone in any field. Here in our part of the world one of the few reasons for extra charges is hard digging because of rock. Luckily, in our area hard digging comes up for less than 20% of all projects.
After more than 40 years of fighting this from every angle we at Fence-All have found the fairest way to handle abnormal digging is to assume and hope that every job is going to be good and then charge a little extra on the projects where it's not. Installers need to make a living, and no one wants to take on a job that they expect is going to take longer than most without any extra pay for their time.
Our rock charges, when they do happen, typically work out to under $3 per foot extra. They are simply meant to compensate for the extra time needed.
New installers who don't know it takes longer to bust rocks probably don't have the tools or knowledge to deal with it properly. The few dollars you save may haunt you for the short life of your poorly installed fence.
Questions? Thoughts? You can reach me at email@example.com. I'm here until Christmas...