Your post could have been written by me soon after we got our rescue dog (a lab/staffy cross). He was exactly the same as your dog when out and about. We found he was aggressive if he was on the lead, which stemmed from feeling vunerable. Off the lead he was not agressive but he did get tunnel vision when it came to other animals. We got him from our local RSPCA centre and were able to attend free training with their staff - all they asked for was a donation of you were happy with the dogs progress. The first thing we tried to do with him was to keep him on a long lead (several metres so he can run free, but still be under your control if required), and to try and keep his attention on us at all time, by constantly talking to him, changing direction and offering treats for good behaviour! We have found that it can take a long time to see results with slightly older dogs, but we are now in a position where we can be more relaxed about letting him off the lead. Most of the time we walk him in empty secured fields when he is very good a coming back to us. We take him to busier locations to try and get him used to distractions. He is now mostly very good at behaving off the lead and not chasing other animals, and happily plays with other dogs now once establishing from a safe distance that they are friendly.
I would have thought that with the help of a dog trainer you and your dog will one day be happily bounding over the hills together
I felt very scared the first time I capsized - my husband was making me capsize to prove that I could get out easily. I thought it would be easy but when it came to it tipping the boat over was really hard. It really helped me not panic when I capsized for real though :-)