If I were to take lumber, and I place a single fence piece, can it encroach on another player's controlled territory? For example, my opponent and I are fully boxed in, and I took lumber, am I allowed to move my fence piece into his land, because it's still connected to my other fence pieces?
Yes you can place a fence piece in an opponent's area. Just remember that at the end of your turn, any fence pieces within other players' controlled areas will be removed.
For example, if your first action was to take lumber and place the single fence piece, then as your second action you could play a fence card for fences in an attempt to fully fence that tile, thus taking control of it. If your opponent defends against your 2nd fence placement then at the end of your turn your single fence piece will be removed as per the rule stated above.
Well, that would have spared some discussion time in my frist Play yesterday. We havent found this in the rulebook, so placing a single fence into enemy controlled territory seemed like a possibility. In the end, we played for over two hours in which seemingly 1,5 were rule discussions.
Now with the clarification it makes so much more sense... but should have been included in the rules.