i have just got a jack russel puppy she is a beauty :)
i also have 3 cats 1 of them has killed all my rodent pets in the past.but now because i have such a small puppy im worried because the cat looks at her like food :( what should i do?

........disguise the puppy as a cat?!!!! ;)
Sounds like your little cat is being a bit of a "I AM FELINE HEAR ME ROAR!".......... some cats are so dominant they will have a go at anything! I'd make sure they are supervised when together until they learn to live with each other and sort the pecking order out.

Yes cats can be trained at any age. ive had dogs and cats all my life and once they know what there allowed to do they gen
stick to the rules. Although it may be harder for a older cat to understand.
but just say no when the cat even paws at the dog . and if the cat carrys on get up and dont hit the cat but push it away and say no. cats have very good brains and learn very quick alot of people forget this.
I do understand that cats do hunt mince and birds ect.. so its natural for the cat try to hunt them. but you need to show the cat that little pup is something connected with you and the cat connects to you with food so he should get the message;)
Goodluck