Cat trouble

We have two kinds of cat trouble in our house. Minnie likes to keep up with world events by helping us with early morning surfing...

Sylvester however merely indulges in early morning suffering at the hands of the new, mean, black cat across the road who ABSOLUTELY destroyed him today. We had to collect his fur from the neighbours' lawn. Please help if you have any suggestions for how to deal with the dark destroyer. He has a taste for science diet... and blood, AND can silently flow through our catflap. What can we do????