Shared fence with next door neighbour

[NimbleBee]

I am getting a new fence and a man to fit it very soon.
The fence up at the minute is owned by the neighbour, it has been up a long time and my dog has escaped through the holes.
Aibu to leave current fence up and put my new fence back to back and not take his old fence down to replace e.g. the partition fence up at present. Or do I ask can I replace current fence?

Ask the neighbour what they'd prefer. But it's fine to put a fence against their fence.

You are not being unreasonable to leave his fence in place and put your own in OP. At least then you won't have the problem of his fence falling down, and him not bothering to repair it, which is presumably why your dog can get through it now.

Well if it's your neighbours fence I wouldn't take it down without asking their permission

I would strongly recommend concrete fence posts which you slot the wooden fence panels in to .

You can ask but if he says no just put yours up against his. But if he then takes down his fence you might have a problem as the boundary will appear to be where your fence is?

You can leave the fence but you shouldn't attach your new fence to the old one. You also risk loosing a few inches of your garden by doing it this way. It be better to talk to your neighbour and getting the new fence put on the original fence line. You would have to agree who was removing and disposing of the old fence. You should also have a chat about who you both think should be responsible for the new fence.

Why don't you ask if they want to replace it and you'll split the cost?