how to stop a male cat spraying?

[CoolC]

We have 2 female cats, but there is a local male who comes in through our cat flap and sprays in the utility room.

Are there any old wives tales that will stop the little so-and-so?

Our cats are old and have never had collars so a magnetic flap is out of the question.

I've seen him in the room (glass door) but by the time I get there to shoo him away the little ninja (he's black) is out of the flap and dissapeared. Grrrr

[rosie11]

Are they micro chipped?, if yes then invest in a cat flap that works with your cats chips.

[parapaul]

OP, I have the same problem - except my visitor(s) spray all around the kitchen, over the bookshelf in the lounge and up the front door. Grrr.

I've tried locking the cat flap but within a day or so of letting my cats out again the visitors are back. Apart from the smell it's a real PITA having to constantly wipe everything clean.