My dog was walking around the yard one day when my friends dog came to stay. My dog started humping the other dog and they wouldn't stop doing it with each other. What's wrong with my dog? Is he different?

I could be wrong, but I think it is more of a dominancy issue than sexual... esp if both dogs were male..

Yes humping is just an obvious one of many ways of showing who is top dog. Females do it too. Dogs also do butt sniffing, head position, eye contact, body posture. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at Raising Your Dog with the Monks of New Skete (http://www.dogsbestfriend.com/) For more on being top dog, see Establishing and Keeping Alpha Position (http://www.dogbreedinfo.com./topdogrules.htm)

Yeah, my husband always thought it would set our old dog into place if he just stopped and humped him one day... LOL... thankfully I never saw him do it..

I could be wrong, but I think it is more of a dominancy issue than sexual...esp if both dogs were male..

Yes they were both males. Thanks to you and labrat (or labman... I forgot sorry!) I have become to know my dog more. It has helped me a lot! Thanks a lot!