Hi, I've just been looking at your photos', wow you've worked hard.
Dogs get everywhere don't they. One of mine would jump over a hedge to get into the neighbours garden and the other would just push his way through I ended up putting up a fence.
I have an idea for your space - I don't know how well it will work though. How about a few post and heavy duty wire and then have some espalier fruit trees planted diagonally and trained along the wire and also some cultivated bramble to train horisontally along the wire. That way you have a bit of a hedge for privacy, a visible barrier to then train your dog not to cross and a good supply of apples and blackberries for pie.
Have fun what ever you decide. The railway sleeper idea sound interesting but watch out for the reclaimed treated sleepers the creosote eventually seeps into the ground, not very organic.
Charlie