quick custom plugin question

[EJ Ciramella]

So I've written a file that stores all the properties set in an xml file
for ant consumption.
 
But running my plugin like this:
 
mvn m2utils:propGen:1.0:propgen -Dinfilename=effectivepom.xml
-Doutfilename=newoutfile.xml
 
It is run every time maven finds a sub module, so instead of having
about 400 properties, I have over 7000.
 
How can I stop this?  I just want it to run ONCE.