Protecting veg beds from cat's digging?

We have always grown veg in pots before now but have recently put in a raised veg bed in our garden and planted out veg which are now beginning to grow through. However, we have a cat and despite using netting to cover the bed, he has managed to get underneath and also sit on top of it, the worst part being that he has dug and used it as a litter tray. clearing this up only solves part of the problem as the digging is the real issue as you can imagine. Does any one have any ideas for what we can use to protect the seedlings and the bed from the cat's digging but also allow for easy watering? Any suggestions gratefully received as we want to ry and get this sorted before the cat digs everything up!! Thanks!