A spaniel and a staffie :)

We have an 18 month old springer spaniel, Watson and have now got a 5 month staffy pup called Molly.

The two of them get along brilliantly. Watson is normally the softest dog ever and well trained (although I know i would clearly be biased!).

He was recently playing out on the green off lead, Molly was out but on a long lead. His friend Ollie (cocker spaniel) was let out of the house and bolted over running straight into watson. For the first time ever Watson took a dislike to his friend (ollie) and growled at him, didnt do anything more but all his heckles went up.

Ollie has previously tried to say hi to molly, following her (she was on a long lead) and her tailed went down. That time watson just looked very frustrated and barked once.

This has only happened since we got Molly! Do you think he is trying to protect her? How do we address it generally?

I would try some separate walks if you meet certain dogs regularly and see how watson manages them on his own

Some dogs get protective over other dogs in the house especially when it comes to male/female. I would try it without Molly as Dave said. It is something you may have to deal with as dogs can bond to other dogs like owners. You could try correcting Watson by keeping him on lead and telling him to leave it when/if he shows any of that behavior. Keep a sharp eye out and watch the body language.