How to tell squid to frequently check if parents are still dead?

WHAT HAPPENS
From time to time squid detects one of his parents as unreachable. The
parent is no longer used and a DEAD PARENT entry is written in the log
file.

PROBLEM
Squid doesn't recognize if a parent is reachable again. This results in
a shrinking list of parents. After a time no parent is reachable at all
and the users get a message like "No neighbors or parents ... ".

ADDITIONAL INFO
squid version: 1.0.18
os: solaris 2.4
squid is run as proxy and accelerator for a CERN httpd 3.0
Received on Tue Dec 10 1996 - 11:21:11 MST