I have a male,neutered tabby; almost 3 years old. Over the past few
months he has started exhibiting rather disturbing behaviour....
He is an indoor cat and I take him out when I can on a leash. He gets very,
very angry when it's time to come in.

Uh....how 'bout getting a litterbox and keeping him inside. Of course if he
starts pummelling at the door, you have another problem. What prompted you to
do the dog thing..you know...put the cat on a leash and walk him like a dog?