In case you aren't already doing it, it also helps to have a global smart list called "competitors" that you can use to build a comprehensive list of known or likely competitors in your database (eg, email address contains x, company name contains y).
Then you can reference this smart list whenever you want to exclude as Kim mentions (filter - member of smart lis, not in competitors) and then you will know you are always using the current criteria. Easy to maintain this way.