The fogs on my old Fiesta mk4 used to get smashed all the time, they were much bigger than the Beezer's though so a bigger target - replacements were about £45 for OEM and I guess the Fester was a much more common car so perhaps easier to get. I paid £30 for a aftermarket one.

I tried to find some plastic covering and in the end went with some stick on plastic (blue peter style) but it didn't help much as there was no gap between the covering and the light - just made the crack smaller than would have been without. I think the beezers fogs are too small for a proper hard plastic cover though... but I would be interested if anyone knows if such a thing is available, as the fogs are very vulnerable!!
 
You can get window film to go in your windscreen to stop stone chips. They also do armerfend (sp?) for head lights so maybe you could try it on the fogs? They do DIY kits
 
always cut one down pretty easy, are leon fog lights diffrent size to ibiza? as I always see cheap leon fog lights on ebay, normaly from wrote off cars.