Lot's of times after studding, males tend to become more territorial, aggressive--especially with other males, they may begin leg lifting to pee on everything in site. Anytime my female was in heat--despite not even living in the same house as our male--the male would sit by the door or window, wouldn't eat, would pace, pee, shake, whine, and got snappy with the other male--not at all fun. When we were sure his time as a stud was done, we had him neutered ASAP.
I also have to agree with another point made...'wanting pupppies' is not reason enough to breed. There is ALOT more to consider before breeding, as mentioned already. I see that you want to breed him just so that you can "get another puppy for free?"
My advice: bite the bullet, save up and buy another one...you will come out ahead in the end.