This is not what you want.
On a model named thing it evaluates to :
(let [tempXXX app.model.things]
(ns temp#).....
This is not good.
You likely want
(let [ns-symbol (symbol ....)] ; I have my symbol, I can return a term
`(do
(ns ~ns-symbol)
(defn hello [] ....))))
Is it working better?
You might want to have a look to already existing Rails like framework
in Clojure.
(I don't know well which parto of any is the ActiveRecord part, so I
won't tell any name, but there is a thread about web development
on this maling list that could be a could place to start.)