Pooping (and now urinating) on couch

Question
My cat is a 2 year old, spayed (since old enough), raised her from kitten.  Recently, the past 6 months, she has been randomly pooping on the couch, no consistent time of time.  She has probably done it 20 times now.  Her cat box is clean, she doesn't have worms, she is healthy.  She cannot see out the window from where she is pooping, however, a male stray cat has sprayed my front porch and possibly other parts of the house outside--could that be related.  A few days ago was the first she has EVER urinated somewhere other than her box.  I've cleaned the furniture cushions thoroughly, tried locking her up with her litter box when we weren't home, etc., nothing will do.  What do you suggest?

Answer
Candi,

She may be reacting to the smell of the tom cat. She sounds like she is marking her territory because she can't get outside to defend it.

The cat may also be telling you that she is upset with someone or something in the home, or that she is upset about her litterbox for some reason. Have you tried a 2nd litterbox in another area of the home? Some cats prefer privacy and don't like to use one out in the open. Try a larger litterbox with deeper litter. Sometimes that will help too.

I am including some links to good articles about improper elimination that you may  find helpful:
(copy and paste or type the whole links into your address bar)

http://cats.about.com/cs/behavioralissues/a/outsidebox_two.htm

http://www.geocities.com/heartland/pointe/9352/litterboxhelp.html

http://www.apbc.org.uk/article10.htm

I hope this helps.

Tabbi