crc function

A desperate newbie question:

I have a _lot_ of tables, where a crc checksum needs to be calculated after every insert/update on all fields (but OID
andCRC). I have no problems writing my external crc function, but: 

 What would be the most elegant way to achieve that? Could I use inheritance in a way to implement a rule / trigger
functionthat calculates  the checksum, and all derived tables would automatically inherit that function? How would the
functionknow about the different columns? 

It would be a nightmare writing an extra function for each and every table. Up to now, the client software is
calculatingthe checksum and iserting the value into the CRC column, but I would prefer to have this function on the
serverside and automatically executed without fail. 

Regards,
Horst