This wouldn't be a separate additional tax; the vast majority of LVT proponents (myself included) propose it to replace property/sales/income taxes (all of which are just economically-inefficient taxes on land anyway: http://www.wealthandwant.com/themes/ATCOR.html).

As for loopholes, LVT is the most effective way to patch them; you can't exactly move land to offshore bank accounts, after all.