We have two lovely older (nearly 9) rescue dogs, male and female
siblings (dark haired lab crossbreeds). We were told that the female
only shows aggression occasionally, notably when her brother is under
threat from other dogs.

The male is fairly laid back with other dogs. A couple of times when
he has gone to another dog, and that dog reacts aggressively, he'll
just walk off but she will make a beeline for the aggressor with a
growl, no attempt to bite though. It's more when she is on the leash,
which makes me think that she may feel more easily threatened or
anxious when leashed. When the other dog is friendly toward them they
both respond quite happily. They're both good off the leash but we
don't want to risk them when near unpredictable roads etc.

It's not really a problem, they both respond to 'leave' or even just
some kind words. Just wondering if you've experienced similar
'protecting' behaviours (which seem perfectly natural to me).

incidently the dogs were being overlooked in the rescue home for
months because they were a pair and because they were older and had
some medical history. It seemed some folk 'score' dogs like you might
score a car on how much rust it has!

They 'get on' fine with our similarly aged rescue cat too, btw! Both
had in previous lives known the other specie and the cat is bold
enough with the dogs, they've settled into mutual ignorance which
seems reasonable.

The male dog does quite like cat food though, but we are not into
punishing dogs for doing 'wrong' (what can that mean to a dog
anyway!), a word seems enough to put him off the thought and if he
occasionally gets a mouthfull i can't really get upset toward him.