To the libertarian, this is a major area of concern and a critical evaluation is needed before any actions take place.
We must first establish the premise that government tends to gradually prey on our liberties more and more. We are like the frog in the boiling pot so to speak. If we assign government a small task, the scope of this task becomes larger over time, and we end up with more regulations and less liberties. Based on this premise, the goal that the libertarian should be aiming at is to extend free speech as far as possible without violating the non-aggression principle.
It is also important to realize how rights work as well. Rights are hierarchical. At the top of the hierarchy is property rights. From property rights stems the freedom of speech and a whole range of other rights. Property rights not only allows the owner of the property to say what he pleases on the property, but it also gives him the power to use property such as billboards and signs to spread his message. In this way, property rights comes before free speech.