We finally got our sand and the round pen is ready for you to use.  Be careful, the sand is new, therefore not as broken down, therefore not as packed, therefore the footing is "heavier" until we use it up a bit more.  I will try to remember to set the sprinkler in it daily, but if you think it's a bit dusty feel free to sprinkler it a few minutes before you use it. 
Rules for the Round Pen are simple:
Limit your use if there is someone waiting to use it after you.
The round pen is not for turn out, you have to stay within 30 feet of your horse when your horse is in the round pen, but your horse is welcome to roll in there, under supervision.