Ducks are amiable creatures but like to have their own space so uninvited guests will be asked to leave with a determined quack and even a quick nip to the ankles! You should be careful with dogs and introduce them to each other slowly. Cats shouldn't bother most ducks but some of the miniature breeds like the Call duck which is about the size of a pigeon would be at risk. If you have cats or neighbourhood cats that catch birds then it\'s worth keeping them away from your ducks.
If you have chickens and would like to keep some ducks as well, this should be fine. But given the chance a male duck will attempt to mate with hens, so it would be best to only keep females. If you have a pet frog, snail or slug then it would be sensible to keep them well out of reach of ducks as they might turn into your duck's lunch!