OS X Mavericks :: Launch Daemon And Routing

The plist file is well launched as a Daemon as machine start up. It starts a shell script which is suppose to change one route in the Mac routing table.

The syslog trace mention that the shell script is well started, but when I check the route, it kept the default route. 

I suppose the problem is due to the fact that the network interface is not up when the script is started at the first time 

If I modify the plist file and get ride of the LaunchOnlyOne key the new route is affected, but the script keep running for ever every minutes.

The plist file: 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "URL">
<plist version="1.0">
<dict>
        
[Code] .....

Info:
Mac Pro, OS X Mavericks (10.9.2), OS X Server