our cats are fighting

Question
We have had a male cat since 1995 (from pound, neutered and all 4 claws removed by prior owner). His ten-year male companions died in Sep 2005; we picked up a female cat (1-2 yrs old) in Dec 2005 from same pound. Both are indoor cats, we take them outside supervised. After introduction issues, they got along fine for eighteen months. They then started fighting, often touched off if the male noticed other cats wandering through our yard, but they continued to fight for days. We've been using pheromones, which helped considerably, but two days ago they began fighting again, for no reason. They can walk up to each other, sniffing and grooming each other, but two minutes later be tearing out fur and caterwauling with no obvious provocation. What can we do to resolve this issue?

Answer
Hi Glen,

You are going to have to try to keep them from seeing outside. I know this may be hard but it is the about the only thing that will quiet this down. Your cats are displaying misdirected aggression. They can't get at the cat in their territory so they are going to attack each other. You can also try to keep the stray away from your yard using mothballs. As long as they see him they will fight. Use blinds or some sort of cover for the bottom of the window they can see him from. This should do the trick along with the pheromones. Good luck.

Ciao, Karen