It's a good policy to implement, Nick....
Takes some monitoring, though... Granted your membership will comply to your policies, I have no doubt... However, the external cross-linking is a harder activity to keep under control, in that "anyone" can create a link, member or not..
You might check with your host to see if they have, or, can enable "anti-leeching"... If so, any cross-linking would be intercepted at the host, and not allowed... I use in on specific directories on my servers. Especially, any streaming directories... Bandwidth is not particularly an issue with me, in that I have no limitations. However, leeping the load to a minimum, does keep the site's response time optimized...
Good luck,
BW@