Advantageous Digging Clauses

Early on when interviewing contractors we heard of someone called an "Advantageous Digging" clause. This is a fancy way to say if the contractor encounters a rock they can't dig up, they're going to charge us more. Given that our backyard, as previously discussed, is 99.2% rock, this concerned us. I completely understand that this is done to protect the contractor from losing money over basically bad luck, but the question became what is the "expected" level of rock digging effort. I mean, you can look at our backyard and see that its going to be filled with large rocks that are difficult to dig up, so we don't want to pay additional fees for poor planning.
The contractor we went with explained his clause like this: If we find a rock so big we can't dig it out or work around it, and we have to bring in a guy to blow it up with explosives, your fee will be what he charges. Not only did this seem fair, but also slightly awesome. I want to see someone use dynamite to explode a giant rock in my backyard! Of course, we don't want to have to pay extra, so we're hoping we don't encounter this situation, but at least it has an upside. Many times in life you have unexpected costs, most don't involve you getting to watch something blow up though. If my water bill came with free tickets to a monster truck rally, I'd probably be less grumpy about it.
Today they dug out what looked like most of the trenches needed for the drainage - which is a lot. Apparently the original builder decided that drainage for our house was completely unnecessary, so all the drains in the front yard and roof, all go to a pipe that is just an open hole in our side yard. This creates our seasonal side yard wetlands which has yet to become home to any endangered species, but does a fabulous job of looking like a swamp. Due to this, our most important task for phase one in the backyard was getting all the drainage put in correctly. This requires digging the trenches really close to the house's foundation (to connect to the downspouts from the roof) which unsurprisingly meant that you could feel every pick axe blow to the rocks they encountered through the floor...while I worked from home.
...type, type, type....ding, ding....type, type, type.....ding, ding, ding...type..ding...*sigh*

After they left for the day I went out to check out the changes and discovered over a hundred feet in new trenches. And in the dead center of the trench closest to the house, sticking up just a few inches from the top of the 3ft trench, was the top of a very large rock. Hrmmm....
Maybe they can work around that. Maybe they just got tired for the day and they'll get it out tomorrow. Maybe we'll get to watch this rock explode into tiny bits!!! mahahahaha...

Heading back inside, I decided to text my husband about the giant rock: