I found this info on indolent ulcers.     Cotton was diagnosed with this last year on his lip.    His tests were sent to a specialist in Tampa.  

This is why it won’t heal   I am pasting this in     I had posted on this b4 but no one could get the link.  This is about an eye ulcer but it is behaving in this same way with Cotton.    I may be able to take him to a good bunny Dr. in a nearby city.   However if it is too big and too deep she can’t laser it.    It has been there 2 years and is very big.   It covers almost all his bottom lip at the hair line one side to the other. 

There was a picture of the ulcer on the eye in this article but it was so so small.   The vets office did say it maybe can’t be done but the vet will have to see him first.   Poor Boo.  Stuck this way

     ’  ”    An indolent ulcer is an ulcer which fails to heal in the expected time. It then tends to cause ongoing discomfort and irritation.

         Eyes affected with indolent ulcers try to grow a new surface skin over the defect, but the incoming cells fail to stick down onto the layer underneath (the stroma). As a result, a thin layer of loose tissue can often be seen surrounding the ulcerated area. The reason why the cells fail to stick is not fully understood but is believed to be mainly because the epithelial cells fail to form tiny ‘feet’ that normally hold on to the tissue underneath.  ‘   “

Thats why the scab keeps growing n growing