What caused your neighbour to deviate way over into your lot ? A few inches maybe, but 5 feet !!! You should have noticed the day they were putting up the fence. From personal experience, get the lot surveyed ! We had ours done, and sure enough, the property line was right smack in the middle of the hedges...out came the chainsaw...anything that leaned into our side, buuuzzzzzzz. It took the crew a day and a half to mark our 50x120ft lot, they had to take elevation readings from other parts of the neighbourhood. The stakes are still in the ground and cannot be removed by anyone, even though we fully paid for the survey. If you are feuding with this neighbour over this fence, do not take the law into your own hands !!! I've heard calls on my scanner about neighbour disputes and the police are very, very quick to respond as these types of incidents can quickly escalate.
This is a very interesting thread, keep us "post"ed !!! Are you able to show us some pics of the fence/property line ? If you prefer not to share, you should be taking some pics for any legal action you may decide to take.