According to the ping man page in Solaris 2.7:

/usr/sbin/ping host  [ timeout ]
[download]

If you specify your timeout to be less, then it will take less time to return after a down router, but then again it may tell you a router is down when it's just not returning your ping very fast.

--xPhase

UPDATE: See rchiav's advice, as Net::Ping seems a better way of doing this.