Netwatch on down log to file

Hi,
I have some problems with my IPS.
Now I want to use netwatch to ping a host and on down write to a file.
I like to have the Date and time in the log file and the IP netwatch pings.
Is this possible and how can I do this?
The lines in the file must be added so the file grows and every new on down message must be add to the file.

you can try to use command :log to log event. in log settings make action to log to file and rule that uses this action