“We live on a dead end street which becomes a small peninsula on a local lake. If our street becomes blocked, ten homes have only one exit for emergencies, and that is to cross one neighbors yard to a private road. The owner of that property wants to put up a fence leaving us no emergency exit. Is there any legal means to prevent that fence from being built?”
Maybe. Your most likely legal route to insist on the right to cross this neighbor’s property (the right to cross and the right to prevent a fence–blocking the right to cross–are pretty much the same thing in this situation) would be if you qualify for a prescriptive easement.
In broad terms, a prescriptive easement arises when someone (or in this case a group of someones) uses another person’s land without permission for the requisite period of time. The use must also be “open and notorious,” such that the land owner would have a reasonable chance to know about it, and “continuous,” meaning not just occasional.
What qualifies for each of these requirements will vary from state to state, as does the requisite amount of time. However, if you and your neighbors have actually been using this person’s property for emergency access for a long time, you might want to look into whether a prescriptive easement has been established under your state’s rules.
Be aware, however, that because of the (purposely) vague nature of the requirements, there is almost always room for argument, and therefore for litigation. Another option would be to negotiate with the owner, and see if you can simply buy an easement. If successful, this would likely result in a much happier neighbor situation going forward.