First, try sitting in the dog bed and having the dog sit next to you. Show the dog the bed is OK and it is ment for them. If your dog is 'food oriented' use treats to persuade the dog to the bed and keep it there. :)

Treats. lure the dog off the bed into his bed with treats and when and if the dog gets back on your bed, scold him and put him back in his own bed and say stay. If he doesn't get back onto your bed give him a treat.

a dog

take him to the vets and get a new dog bed. simples.

The dog has probably buried something in it's bed and doesn't want you to find it. My dog does that quite often.