When I installed Industrial Garage Doors we had to do projects like this all the time (on concrete not rocks).
You will need a Rotary Hammer Drill.
You will need to use a Carbide Tipped Core Bit. They are used to create large holes. You will also need a chisel bit to blow out the core.
The cup of the bit will only drill about 3" deep. At that depth, the bit is removed from the hole, the core busted out with chisle and removed, and then the bit is reinserted. Repeat until you reach the wanted depth (18 inches for DGA sleeve).
The bad news, unless the city has one, is that a 5" diameter by 22" deep bit are around $350 dollars and a 4" diameter by 22" deep bit (I don't think a 4" inch bit would allow much room for crete) would be closer to $275. Not cheap, but the most effective way to put a nice clean hole in concrete or a rock w/out cracking it. You may want to ask around to find a concrete dude or company that would donate tools and time for sponsorship on that hole.
This is what a bit looks like.
"I'm not impressed with aces of any kind. 95% of the time, they're just bad shots that got lucky and happened to hit the chains. Otherwise, they'd have sailed 50' past the hole." ~ Cydisc