Is this a threat? Dogs on property?

You can't threaten property which is what dogs and cats are. You can only threaten people. A witness would be of no help to you and you can't take someone to court for threatening property. Only if something happens to the dog that would fall into animal abuse could you complain to the police who would be the people to file charges, not you. A witness to animal abuse would be fine. A witness to an upset neighbor who told you to keep your dogs off their property is useless.

Remember, the person who's complaining who sue you in court for letting your dogs go on their property and cause them problems. You are in a lot more danger of having to go to court for not controlling your dogs than the person complaining is.

What are the leash laws where you live? It is possible that you are violating law by not having your dogs on a leash and/or on your own property

he has every right to ask for No Trespassing on his property... that would include You & Your Dogs

I would not recommend taking him to court... you need to keep yourself & your dogs off his

If he said: "If I ever see your dogs outside then I will shoot them"... or if he was saying: "the next time your dog is in your yard and looking at my yard, I will shoot them".... then those statements (where the dogs are in your yard) could be considered a threat

What he said is not a threat because it is in reference to his own property

You are required by law to keep your dogs on a leash. If they are not on a leash then you have broken the law. If while not on a leash, they go into your neighbors yard, then he has the right to do something about that. He cannot kill them unless he is actually threatened by your dogs (growling, snarling, acting as if they might bite him), but he can certainly snatch them up and take them to the pound. If they harm him or destroy his property, you are legally liable for that. You will have a hard time convincing a judge your case against your neighbor if you allowed your dogs to roam free onto someone else's property.

You have to keep you dogs on your own property, if they are on his property then he can say he needs to protect himself and shoot them, and if he gets hurt by your dogs, then you are in big trouble.