This defines multimethods, and the other implements them

a.clj

(ns a
  (:use m))

(defmethod foo :a [o] (str "a-method for " o))

m.clj

(ns m
  (:require a))

(defstruct ob :baz :bar)

(defmulti foo :baz)

The problem:
I would like to put defmethods in separate files, depending on dispatch value (:baz).
I'd like to be able to add new implementations (files) for new :baz values, so my methods are extensible.

In this example I'd like to be albe to
(use 'm)
(foo (struct ob :a 123))

but this will not work, since there is a circular dependency.
On the other hand when I'll remove (:require a) from m.clj, I will have to do
(use 'm 'a)
(foo (struct ob :a 123))

and if I add new implementations in b.clj, I will have to change all my files to: (use 'm 'a 'b)

How should one handle this use case?