How about this, R1ch999999,
Assuming your section of fence isn't a "propery-line" fence, I would recommend you:
- Give them a bill for 1/2 of the shared segment of fence;
- along with a document from a lawyer indicating that they have placed their fence on your property and that by you allowing this to happen you in no way are giving them any ownership rights to your property, either stated or implied; furthermore the document should state that they are resonsible for the maintenance of their side of the fence; ask them to sign the document.
If they are unwilling to pay or sign, ask them to move their fence.
You might consider this approach, and as I think about it, it is very fair.
Another approach is to TALK to them about the very same thing. Ask them to pay for 1/2 of the fence and maintain it. If they ask "WHY", then calmly explain that you can't maintain the fence now since you can't get to it, and they are clearly using 1/2 of it...
(or do I misunderstand the issue, are they only using ONE corner?)
TJR