What is correct way to enable watchdog?

[Peter Steele]

We have our systems configured with the watchdog enabled, with /etc/rc.d/watchdogd defined as 

. /etc/rc.subr 
name="watchdogd" 
rcvar="`set_rcvar`" 
command="/usr/sbin/${name}" 
command_args="-s 10 -t 300" 
pidfile="/var/run/${name}.pid" 
load_rc_config $name 
run_rc_command "$1" 

We assumed this would give us a watchdog timeout of 300 seconds (5 minutes), meaning a system would not reboot unless it is non-responsive for five minutes. However, in a recent stress test we had unexplained spontaneous reboots on two systems, with no logs of any kind to indicate why the systems rebooted. 

Do we have something wrong with how the watchdog should be configured?