Containing the dial-up problem is conceptually easy: by installing the Remote Access Server outside the firewall and forcing legitimate users to authenticate to the firewall, any access to internal resources through the RAS can be filtered as would any other connection coming from the Internet.
The use of a TACACS+ Server by itself cannot eliminate hacking.
Setting a modem ring count to 5 may help in defeating war-dialing hackers who look for modem by dialing long series of numbers.
Attaching modems only to non-networked hosts is not practical and would not prevent these hosts from being hacked. Source: STREBE, Matthew and PERKINS, Charles, Firewalls 24seven, Sybex 2000, Chapter 2: Hackers.