My Dog did something odd recently...

Question
Well usually when he gets really excited about something he will pee.  But this wasn't the case, one of my friends came over today, a female, and she was petting my dog and he just hiked his leg and peed on her on purpose, what was he doing?  I mean he raised his leg and everything, this is very odd for him.  I hope you can help me out, thanks

Answer
Some dogs pee on people to show they are thier property, but if he doesn't except when he is excited this isn't the case. Make sure you don't let him sit on the sofa, feed him after you eat just to prove you are dominant over him. Also you should take him to a vet or ask a vet on this website if getting excited makes him want to pee.
Good luck...