[jah271]

We have an 8 month old female GSD. She is lovely off the leash, plays wonderfully with dogs and is great with people, but as soon as we put her on the leash she is lunging and barking very aggressively towards other dogs. It's really awful. If a dog does come up to her she cowers away. We are thinking of getting some help for this (v expensive....).. any advice would be massively appreciated as I'm getting worried she is going to get aggressive eventually.

 

[MaggieRoseLee]

Weekly dog classes shouldn't be that expensive when you break the total cost up over all the 6 or 7 sessions. I prefer a good set of group classes (usually Petsmart type aren't the best) and I go for 6 months or more. It's amazing what I learn... and then how suddenly my pup starts behaving and learning too

Group classes end up the best for me because it's the best mix between socialization (in a safe environment so dog get confident) and training.

If you live in PA I can recommend a place in the northeast https://www.letsspeakdog.com/

 

[Malibu]

8 months old you should take Maggieroslee's advice and get her to training classes. Should be an easy fix if you go now..

 

[McGloomy]

Do research on 'Leash Aggression.'

 

[Apex1]

I wouldn't call it aggression unless you know for a fact your dog is aggressive. I believe OP stated the dog is social. It is reactivity. Leash reactivity is really frustration. Off leash the dog is probably impulsive. Speaking from personal experience.
Reactivity typically has a genetic component. It may be a bit before another runs, but the Collared Scholar just ran a beta reactivity boot camp for 30 days. Not a solve reactivity in 30 days but give you the tools with support over the course. I participated and I'm truly impressed with what we have gained so far. Just incase you don't find a class as suggested above, I thought I would put that class out there. I'm pretty darn confident that I will end up with a reformed reactive dog.