Jelousy

Question
I have two dogs from the same litter.  One was raised separate from the other for the first 6 months.  They were reunited about 6 months ago and one is very jealous of the other.  In fact, whenever I pet the other dog, the jealous dog bites at his legs and ears...playfully, but escalates into rugged play.  I am fearful it will eventually turn into an out and out dog fight.  Any suggestions?

Answer
Get both of these dogs into ongoing obedience classes (several months), work with each separately every day, and start practicing "Nothing in Life is Free" with them. http://k9deb.com/nilif.htm  They both need to know that YOU are the Alpha and will not tolerate that behavior, and you need to learn how to assert yourself more so that you can stop this behavior as soon as it starts.

If they are different sexes, they will probably be fine. If they are the same sex, it may well escalate into more. Make sure they are both neutered, as that will tone down those hormones a bit.