My friend is C. is redoing her closet, and her pets love the cozy space where the clothes end and the floor begins. However, this is frustrating for C. when she is trying to get ready for work and her clothes are covered in hair.

I suggested she get something to deter the cats from entering the closet - like a plastic runner, (you know, the kind all the grandmas use to protect their carpets) . . . . only you'll want to turn the runner upside down. I cant imagine those hard little vinyl bumps would be pleasant for kitty's tender little pads!
And old chair mat would accomplish the same thing. I've also heard that cats dont like the sound or feel of aluminum foil so you might try that too.
Dont worry about denying them this little hidey-hole . . . your critters will find PLENTY of other places to nap!