If you want to stop your SharePoint site users from opening the site in FrontPage, you can add attributes to the Project tag in the ONET XML file and either limit their actions or stop capabilities completely.
For more information, reference the following Microsoft articles:
http://support.microsoft.com/default.aspx?scid=kb;en-us;831612#7
http://www.microsoft.com/technet/prodtechnol/sppt/reskit/c3261881x.mspx (Table 32-2)
I have done this and it works well. One thing to keep in mind especially for production servers, is if for any reason you need to open up the site in Front Page, you have to remove the attribute(s) from ONET.xml and reset IIS for the changes to take effect.