building fences from the craftsman's tools.
just don't build higher than the synagogue roof
(discussion of previous mishna finishes with a warning that in a city the houses' roofs shouldn't be higher than a synagogue. A new mishna prompts a discussion about items that various craftsmen should not wear/carry on their person - often in their ear - close to shabbat, lest they come to carry them on shabbat. building fences around the law. for english translation of the full talmud page see here)