i have a pit bull... he leaves them alone... lets them roost on top of him... maybe because he's the laziest dog on the planet... but he hates my muscovy duck... i think because of the noise he makes... but still... it depends how you train him... and getting an older dog sounds kind of like a bad idea to me... what if the person before trained him to chase a toy chicken...? the reason my dog hates the duck is because i trained him to chase a cat or bark at anything when i make a hissing noise... duck hisses, and now he hates duck... i can't stop it... i have to get rid of duck...