What happens if someone objects to you fencing off uncl aimed land during the adverse possession period?

How do you know its really unclaimed?

What happens? That person would take you to court. If he or she does have a valid claim to the land, the adverse possession period would be tolled.

In the US? You know of land that is unowned by either a private party, corporation, town, city, county, state, or the feds? I'd be surprised. Have you looked at the deed maps in your town hall?

As for adverse possession of owned but unused land (which is probably what you mean), your fence would have to be 'openly hostile' for the minimum number of years in your state (many are 20).
I have seen brick walls installed one day and torn down by the rightful landowner the next. As long as he is confident that it's his land, he doesn't have to mess around suing anybody. The burden is on the tresspasser/encroacher.

In the US? You know of land that is unowned by either a private party, corporation, town, city, county, state, or the feds? I'd be surprised. Have you looked at the deed maps in your town hall?

As for adverse possession of owned but unused land (which is probably what you mean), your fence would have to be 'openly hostile' for the minimum number of years in your state (many are 20).
I have seen brick walls installed one day and torn down by the rightful landowner the next. As long as he is confident that it's his land, he doesn't have to mess around suing anybody. The burden is on the tresspasser/encroacher.
And most places they have to actually be paying the property taxes.. including arrears etc...