How Do You Get a Cat to Stop Shitting on Your Floor?

[Stratego]

I currently live in a two story house, and my housemate who lives downstairs has a cat. The cat keeps coming upstairs to shit, and I don't know how to get it to stop.
1. I clean to floor so it doesn't smell like shit. The hope is that I get rid of any traces of cat shit smell so that the cat doesn't think it's a place that it should shit in. That doesn't work.

2. I've been informed that if a dog shits, you should catch him in the act and shove his face into the shit so he knows that it's wrong. But this cat shits when I'm at work and I can't do this.

3. I tried putting a fence, but since it's not my house I can't fix a permanent one. I use one that I learn against the stairs, but sometimes the other roommate take it off and forget to put it back, and the cat shits upstairs.

Short of killing the cat, what are the ways to get it to stop shitting upstairs? It can shit downstairs for all I care, just not upstairs.

[Winchester]

Move the shit to your housemate's bedroom.

[The Comrade]

throw the cat away

[Spider]

1. Acetaminophen. Its cyanide for cats.
2. Put the corpse in a gallon jar.
3. Add lead fishing weight. Secure lid with marine adhesive.
4. Throw in nearest body of water.
6. Make a lot of sympathetic noises when cat turns up missing.
7. Profit.

[gla22]

Get a spray bottle and fill it with water.

Spray your housemate in the face whenever his cat shits in your room.

[Dylan]

[Dylan]

Also never do that to a dog

[The Dharma Bum]

I usually move

works pretty good

[jimmyz]

Place two of these at 45 degree angles on each side of the top step of the stairway.

http://www.petsmart.com/product/index.j ... lInUS%2FNo

[The Dharma Bum]