I'm unsure if I can going to get shot down in flames for posting this, but I need help.

Daisy is a 4.5 year old cross-breed, spayed. I have had her from 6 weeks old, from the NCDL. We also have a 2 year old labrador.

Daisy is as good as gold indoors, she's never been a problem and has never shown any aggression towards the family.

About 9 months ago, she started to show dog-aggression whilst out on our walks, and once bit a collie on the nose for no reason (she didn't draw blood). She will sometimes try to "nip" our labrador when out on our walks too, for no apparent reason at all. Somet days she is fine, other days she is like this.

BUT, this morning, for no reason I can think of, we went to walk past a young lad (about 17yrs) and Daisy bit him. She bit his leg (once, in one place), but luckily he had jeans on so the skin is bruised but she didn't draw blood (but did rip his jeans) and she caught his finger. I took the boy back home with me and made sure he was OK etc, he kept saying he was fine and I put a plaster on his finger and made him a cup of tea etc.

Obviously I guess I now have the possibility of the police knocking on my door - what is the situation if this happens?

BUT, more importantly, I clearly don't want this to happen again. I am going ot muzzle Daisy before she leaves the house in future for obvious reasons, but I know this isn't solving the problem but only masking it.

I would add, for everyone's benefit, if I had any doubt that Daisy would hurt one of the members of the family then I assure you she wouldn't be here, truthfully. Her aggression/anger whatever, is limited to outdoors.

Can anyone give me some advice?

I have tried to contact the only two behaviourists I have found in my area - one is off sick, one has waiting lists of 8 weeks.

Thank you