I may be wrong on this but I think that on the typical free sites, you are unlikely to have that sort of control. You could put the page(s) in question in a folder with a weird name and make sure those pages contain no links directly or indirectly to pages with links that are off your site and not publicising those URLs anywhere.

This is not restricting access but making those pages hard to find and I don't know how well it works in practice. One other thought along that type of route, is to ensure every directory has it's own default page if needed. Some sites will give full directory listings if such a page is not present.

To give an example of what I mean, using my site, www.jonbanjo/forum (/) is not a web page but a directory. The way I am set up when no page is specified, the system looks for "default.asp" within that directory and depending on its presence either displays that page or produces an error message. Other systems are quite capaple of saying "let's just display the directory of www.jonbanjo.forum/".

Jon