The Wikipedia article on geolibertarianism gets one nuance slightly wrong. Geolibertarians don't necessarily believe that all land is an unownable commons. Rather, some of us simply take very literally the Lockean proviso that homesteading an unowned resource (e.g. virgin land) must leave "as much and as good" for others. So we say there would be zero land value tax on you if there is available to others "as much and as good" land as that which you monopolize -- or if you allow the community to use the land you squat on in the same way that you use it. The land value tax only kicks in when monopoly rents are earned due to the Lockean proviso being violated. Such rents are a violation of individual rights under the Lockean analysis, and are thus aggression. The geolibertarian land value "tax" is not really a "tax", but rather is reparations for this aggression. (A LVT does not tax site improvements like buildings etc.)
Geolibertarianism thus solves the central conundrum of minarchism: how to finance the protection of life, liberty, and property without initiating force. Its solution even offers an unanticipated bonus: a non-force-initiating libertarian safety net for the poor. Geolibertarianism points out that in the state of nature there is always marginal but productive land available for use by the destitute, and that faithful historical observation of the Lockean proviso (leaving "as much and as good") should have always ensured that this remained the case even to this day. To the extent that it is no longer the case, excluding people from access to the natural productive opportunities on what used to be the commons is unjust -- i.e. is aggression. Therefore, where land is scarce its "ground rent" should be considered part of the commons, with each individual having an equal claim on it.
Technically, "ground rent" is is the excess production obtained by using a site in its most productive use, compared to the production obtained by applying equivalent inputs of labor and capital at the most productive site where the application doesn't require (additional) payments for use of the site. In other words, ground rent is the advantage you get from exclusive use of a site compared to the most productive available site that is not in use.
For more information, see my site http://ecolibertarian.org/.