Is 'marking' a common possibility when entering a new cat into a household with a cat?

Well, I am seriously thinking of bringing a cat home from the shelter on Sunday. My roommate is Ok with it. She has a three year old female calico, and the cat I want is a three year old all black male. He is fixed, I believe my roommates cat is too. The calico is sensitive, but has relaxed around me, and the black cat, still at the shelter, is friendly... I held him both days I was there, and he let me hold him on his back yesterday. Both my roommate and I are eager to get the cats acquainted, and think putting barriers up to protect them is almost a bad influence on the scene.

I guess I wish for some experienced cat people to comment on what makes cats 'mark', how can I prevent it.

Also, it seems proper to let my possible new cat hang in my room for a couple of days to let him understand where His space is, also to adjust to a new setting and home... but when do I know it is right or wrong to meet the other kitty? I am going away for Christmas, my roommate said she would care for the kitty while I am gone, and i am hoping it doesn't put too much stress on the new cat, but I want to get him out of the shelter. We will be getting him on Sunday.

Thanks to everyone for posting threads and replying... sometimes so fun to read through even if the cat story doesn't pertain to me, yet.

Hi and congrats on getting a new kitty 

In answer to your thread title, no, assuming both cats are spayed and neutered, it is not common at all for them to 'mark' their territory when a new cat is introduced.  It is not impossible, either, but it is not likely.

I highly advise, however, that you introduce the cats according to the steps in this article: http://www.thecatsite.com/a/introducing-cats-to-cats   They will need to be kept seperated, possibly for weeks or longer or possibly only for a few days.  It really depends on their reactions. Hopefully someone more experienced in introductions than I am will chime in

THank you again for adopting a kitty.