Counting Number of Records on CDO per Lead

Hello,

We have a one to many relationship with a CDO.  I want to be able to count/identify the number of records are on the CDO for each specific lead.  Is there a best practice way to do this accurately? 

Currently, I have a smart campaign set up that is triggered by "Added to CDO" and then in the flow step I change the score to +1....in theory, every time a record is added to the CDO, we will add 1 to a score field.  Obviously, this is a jerry-rigged idea, so please let me know any glaring problems with this set up and if there is a better or easier way to do this.  (Records on the CDO will never get deleted, so we don't have to worry about subtracting the "score")

Thanks!