I find the free add-on ApexSQL Search useful for finding procedures (or data) in database(s), but you could use the below query as a starter to search stored procedure definitions.

select objects.name,
     sql_modules.definition
from sys.sql_modules
     inner join sys.objects
         on sql_modules.object_id = objects.object_id
where sql_modules.definition like '%Dutiable%'
Andrew P.