I have been digging a french drain to drain water away from the back wall of the house where I am putting a small patio. I am really getting tired of digging and have 20 feet to go before I get outside the fence where I can leave the end of the drain pipe exposed without risking the dogs getting in it. Just hit a big rock, sigh. Can I put a big gravel pit around the end of the drain and bury the whole thing underground, or do I need to pretend I am on a chain gang and keep digging to where I can bring it out with an exposed opening that
would drain onto the grass?

Can’t imagine why you couldn’t use a big gravel pit at the end. Just more digging! If you cover it over you have to use something so the soil won’t mirage down into the pit and make it less than useful. If you open end it be sure to put a grate or something to keep critters out of it. Mice etc would love to set up camp in side. I used plastic caps that had little squares cut into them to cap mine off. using a couple of screws to hold it in place. They are like a drain cap you see in the floor. I am sure they have a real name but can’t recall it right now.

Personally i would extend the pipe to drain to daylight if possible. you can install a dry well to handle that water, but again more digging and expense–but more effective than a rock pit. I’ve had an idea here lately that i would tap into the french drain and run a pipe to my heat pump, install a plenum around it and attach the pipe to the plenum. the thought is that warm wet air would be pulled through the ground cooling it, and then through the coils of the heat pump, increasing the efficiency of heat exchange.