@tvinke warns you about an issue you are going to face in any medium to big size Grails project:
You are going to have a lot of Services.
He advocates placing classes such as Builders, Factories, Helpers in src/main/groovy. Then register those classes as Spring Beans. s
He shows how to declare Spring Beans two ways: in resources.groovy or with Component Scanning.
If you don't want to get rid of your services, consider at least two things: A good naming convention across your team (I like suffixes, e.g. GormService ...) and proper packaging.
Dynamic finders have a clear advantage. They are easy to understand, they are readable.
@tvinke cautionary tale encourages you to centralized them in Services.
if all of the queries are in a neat, well-defined place for everyone to see and go to, the most likely it is that team members will default to basic human behaviour follow the defined path, and color within the nicely defined lines of that part of the codebase