Chimney Pots: Do you have them, have you looked at them? Chances are they are cracked and need replacing. It used to be your only choice was to scour the salvage yards and then finding a good one is always problematic.
Fortunately, there is now a good resource for chimney pots called Chimneypot.com
They have 45 styles of Victorian era chimney pots plus ones for modern applications. They also have rain guards available too.