Krakker

If you happen to be savey enough to replace your water pump, you'll appreciate this tip.
Most water pumps come with spanner holes on the front of the flang to keep it in position while you tighten the 4 bolts keeping the pulley on the pump.
I recently ran into an issue where a new pump did not have the spanner wrench holes. (on my 99 XJ Sport)

Water Pump Pulley Tip:
Simple enough tip tho, get out the drill and a bit of your choice. It just needs to large enough to get a (what ever you want) through the hole. I picked a spot near the crease and at a halfway point between the bolt holes and drilled through the pulley. This is pretty stout material, NOT precision or balanced and the hole will NOT effect it's function.
After the hole is drilled, clean up both ends of any sharp burrs on both sides. Install the pulley and bolts, insert what you intend to use through the hole you drilled far enough that it keeps the pulley from turning as you tighten the 4 bolts.
remove when done, install belt and happy Jeepin'.

Broken Bolt head fix:
If you happened to snap the head of a bolt, (any bolt for that matter) You may have options to remove it that won't require drilling or other messy tactics.
1st: if you have enough threads, you can run a nut down to the face of the surface, (use penitrant if you have it too) then run a 2nd nut down to the 1st one, make them tight together.
Now get your wrench on the 1st nut (near the face/surface) and give a smack with a hammer or mallet (untightening direction) see if you can now loosen the bolt and get it to come out. If this works, clean up the thread holes before reinstalling a new bolt.
Some things like water pump bolts, etc. should just be replaced if they've been on there for ever. Don't skimp on cheap stuff, if your spending your time and money on good and/or important parts, go a little further and get new bolts for them too.

NOTE: Squeal after belt, etc. change. After changing all, or what ever you replaced and have reinstalled your serpentine belt, if you get a GOD AWFUL squeal, or just a squeal when you give it gas and the A/C is on, you most likely will need to tighten your tensioner a little more. I personally ran into this after doing an entire cooling system upgrade. A/C worked fine before, and after, it squeeeeeealed like a pig. (pun intended) I sprayed a little WD40 to dress the belt and it went away until I engaged the A/C. You'll need to tighten it enough that it doesn't squeal when stomping on the gas. The belt should twist just enough to inspect the ribs. Either way, tighten till the squeal does not happen.
There needs to be enough tension on the pulley for the clutch to engage properly. If not, the clutch wants to stop the pulley from turning and the belt will screech like a gheto Cadillac with a shot power steering pump.