Lemons
Clean the hob with a lemon-scented cleaning product, preferably one that leaves a strong lemony smell behind - cats hate the smell.

If you can get one in an aerosol can so much the better. Use it when the cat is present, they also hate the hissing sound. Over time the cat will associate the hiss with the can and won't go near it even when empty.

Leave the can of aerosol lemon-scented cleaning product in a place you don't want the cat to go.

(EDIT) Bonus Tip: After following the above, if the cat is doing something and you want it to stop, e.g. climbs on the table, scratching the furniture, etc. simply shake any nearby aerosol can, jar, or even your empty fist in the "wanker" gesture and it will stop what it is doing and slink off to avoid the hissy spray. (Assuming you always shake the can before use like you are supposed to).
( Amos E Wolfe makes vinyl signs and things like that, Mon 27 Apr 2009, 22:15, 1 reply, 16 years ago)

Thank you!
They have already learnt the 'shaking motion' (via deodorant) and scarper when anything like that is shaken. The problem is, I'm not around when they do the peeing! I will def give lemons a go, but have already tried orange peel.

To save another answer I've already tried tin foil. It only works on 2 out of 3 cats. No.3 is quite happy to piss on tin foil despite a) the noise. b) the puddle around his paws. He just shakes them off against the wall leaving spray marks.
(Big Smurf Brush me daddy-O, Mon 27 Apr 2009, 22:44, Reply)