I am staying with a friend for the month of August and his house is right down the street from the Montgomery County detention center in Rockville. Is there any silly law which would preclude me from keeping a handgun or AR15 with me at his house? I'm not carrying it outside or anything, I just want to have it near me at night when I sleep. I can't imagine why there would be a law against this, but one never knows in MD.....

I used to live right down the street from that place and the MSP barracks on Montrose.  I had my firearms at my house stuck in between 20-30 liberal democrats for 3 years and they only gave me crap once about my hobby.  My neighbor asked what was in the bags as I moved out and I told her my guns and she tried to give me a earful but I was on my last box and then I was out of there.

Cant help you any with your question about staying at anothger persons place.

Joe

IIRC, pay him a dollar for rent and you're in the clear.

Kharn

Since you are "staying" there, I think it would be considered your residence.  Like Karn said, pay him rent and you should be  good to go.

I think you will need to file paperwork only for a class 3.

I'm pretty sure i'm right on this. As long as you are an invited guest you are in the clear.