poorly medlar

We've got a medlar tree in our garden which is - I think - suffering from a fungal disease caused - possibly - by our cats scratching at the trunk.

Does anyone have any suggestions how to a) cure the disease and b) stop the cats scratching at it? Please email any suggestions!

medlar leaves & trunk.jpg
some leaves & part of the trunk (79k)
medlar leaves 2.jpg
new leaves (56k)
medlar leaf.jpg
a mature leaf (77k)
medlar leaves.jpg
more leaves (62k)