sounds like you've thought long and hard about a rescue dog and to me you would be a perfect candidate. cindere's suggestion sounds fab about the gate, and also if you're upfront with the rescue then i would think they will take all things into consideration
we have a similar problem but the communal path runs between the 5 terrace houses and the gardens PLUS we have a stream at the rear of the gardens so it is really difficult to try and secure - hence my reticence (plus an entire male boy) in getting a rescue.....
having said that, my immediate neighbour now has a rescue dog despite the garden situation. the dog isn't out there unsupervised anyway and my neighbour has given this boy a loving happy home so in some situations it can work.
Really really hope you're able to find a cocker to share your lives with - they would be a very lucky pooch