I'm not advocating anarchism.

I ask, because this argument about the "proper role" of government tends to start growing all kinds of exceptions that expand the role of government the moment someone starts taking it to its logical conclusion and argues for removing protections of exclusive access and use of land in particular, as a means of maximising liberty by removing government enforcement of artificial monopolies.

Most countries even today do have substantial exceptions to private property rights for the purpose of increasing liberty for society as a whole (e.g. granting access to natural resources to society as a whole).

I think government should enforce all private property rights, although perhaps at an indirect level (e.g. you still have to lock your door, but the government ultimately will punish people who break in).

However, the question of what is a property right and what is not is germane.

argues for removing protections of exclusive access and use of land in particular

If two people can do something simultaneouly without one initiating force against the other, then property rights don't apply. Sometimes it falls to the legal system (e.g. convention) to stipulate the precise boundaries.

For example, if a utility company wants to run power lines below my land, then unless that prevents me from doing something underground that I'm already doing, I think they have the right to do so, as long as the lines can be installed without causing me significant inconvenience (and with proper forewarning).

So, basically, you establish property rights by actually using the property in a certain fashion.

have substantial exceptions to private property rights for the purpose of increasing liberty for society as a whole

I think that's a false example. Society is just composed of individual people. If you take away one person's rights, it may increase somebody else's access to something (e.g., say, birth control), but it does not increase _liberty_.

(e.g. granting access to natural resources to society as a whole)

I don't really see how natural resources _wouldn't_ be available to society as a whole.

That's where you'll get disagreements; your reasoning doesn't apply if the exclusive access and use of land isn't considered an artificial monopoly. Particularly, 'artificial' is usually defined as something man-made, yet property rights are extremely common among other animals as well, even if they haven't developed a moral framework to justify them.