DNS Poisoning

One common attack is DNS poisoning, where a DNS entry is modified to send traffic to a host controlled by the attacker. This can occur at multiple points along the search path used by a host to revolve a host name to an IP address, one of which is the local hosts file. What kind of measures could you take to ensure that the local hosts file is accurate? Be sure to bring in at least 2 outside sources to defend your answer.