Hi bonga. i know exactly what you mean and it's a real pain in the rear! The same thing happened to my wifes Punto before christmas. I tried all manner of ways of securing them but because it's a rotating joint, nothing worked. I finally resorted to using those elasticated luggage straps with the plastic coated hooks on either end. I hooked one end under the pushrod of the wipers and stretched the other end over the air filter intake clear of the hot rocker cover and hooked into the body cavity near the base of the vertical coolant expansion tank.
That was before christmas and she's driven virtually everyday sometimes in heavy rain and they haven't come off once. It doesn't look very pretty under the bonnet, but it sure works. It's a bit 'makeshift' I know but the alternative probably isn't cheap!
This is the type of thing I mean available from focus / b&q / halfords etc:
http://www.focusdiy.co.uk/invt/197327&bklist=
I had to put tape on the rubber seal that runs the width of the engine bay near the wiper motor where the straps cross it to avoid chafing. If you need clarification I can send you a photo.