defmulti+, an enhanced version of defmulti that unmaps itself from the ns when present. Eases the pain of redefining the dispatch method at the REPL.

defmulti-enhanced.clj

(defmacro defmulti+ 
  "An enhanced version of defmulti that unmaps itself from the ns when present.
   Eases the pain of redefining the dispatch method at the REPL."
  [name & args]
  `(do
     (when (resolve '~name)
       (ns-unmap *ns* '~name))
     (defmulti ~name ~@args)))