Ok, to start out - YES to the clicker! My dog learns 2x as fast with the clicker. It's simply an indispensable tool that almost every animal can benefit from being trained with, IMO. I highly recommend that you use a combo of a Halti attached to a martingale collar. The Halti will give you the extra control you need right now and a properly fitted martingale cannot be slipped out of.

A few things this dog needs to start learning ASAP - obviously, you'll first need to work on getting her to associate the clicker with a treat, which I usually like to do over a few days so the idea really solidifies. She needs to learn "watch me", or "look", the latter is the command I prefer. I taught my dog simply by holding a treat between my eyes and clicking when he made eye contact. You can gradually start asking for longer and longer eye contact, but like all training - don't overdo it.

You need to start teaching her to heel as well. The video I provide in a few paragraphs includes that.

If your dog is not taking a treat, that means you've allowed your dog to get over-threshold. I've attached a link, but I will sum it up quickly - that essentially means that you've allowed their fight/flight instinct to kick in and when that happens, the dog will not accept treats and learning stops. The key to working with a leash reactive dog is absolutely to keep that balance of exposing them to the trigger and keeping them sub-threshold. But I will briefly explain a few ways how, and attach some links for further reading on the subject.

Ok, here's a link that will help to read first, as it explains the basics of the issue - http://www.4pawsu.com/onleashaggression.htm

You can take a slightly more traditional path and teach her to focus on you around the trigger and *gradually* start exposing her more to the trigger every session, constantly keeping her sub-threshold. To do this, you'll need some high value treats (warmed up veggie hot dogs is my dog's food of choice ) and you must be very interesting and energetic during training. You need to be very in tune with her body language and if she loses focus on you, you need to turn and refocus her quickly. Here's an example of this, with a dog that is very dog aggressive on leash. Watch it with the sound on. Personally, I don't know if I'd ever use that much pressure with a head halter, but it provides a clear example. It also shows how to lay the foundation by teaching them to heel.

My personal favorite is Behavior Adjustment Training, or BAT. It's an excellent method that I have found great success with. The best thing about it is that it equips the dog with their own tools to control their environment. That's all the dog is really trying to do when they lunge and bark - they are insecure and need to control their environment, and the only way the know is through lashing out. What we need to do is teach them an alternative way to respond. The link may be a bit complex to start out with (It took me several reads and trying the method myself before it "clicked" in my brain.) Make sure you watch the videos, too, as they help.

I really didn't do a great job of explaining these things, so if you need me to explain further, just ask. I could write about this for many paragraphs so I tried to keep it as short as possible.

I hope you can successfully get Miss Cassie to not react negatively on leash, however you choose to go about doing it.