Hahah, I sometimes think Leroy is a bit dimwitted too
I still love him to bits though!
For those of you working on the come when called…. Initially start with some treats, and sit with the bunny. Just feed the treats to the bunny and every time you give him/her one, whistle (or make whatever noise you want to signal “come” – I’ve found that a distinct noise is better than a word for this command). If your bunny already comes running at the sound of the treat bag, rustle that and make your noise so eventually the bunny associates your whistle (or whatever) with the treat bag and with running to you, so then you can phase out the treat bag sound. Do that for a couple sessions, then for your next few sessions, show the bunny the treat, move a step or two away from the bunny, with the treat clearly in view, and make the same noise as the bunny is running to you. You can gradually lengthen the distance, and then move out of sight to another room or behind a couch or something and they’ll seek you out when you make that noise. Once you reach the point that they come when you call them from another room, you can back off the the treats and go to giving them treats on a variable schedule…. so sometimes they get a treat when they come and sometimes they don’t. That way they’ll continue to come to you in the hopes of getting a treat. Psychologically, a variable reward schedule actually strengthens the response and is better at preventing “decay” (un-learning the trick). Why do people continue to gamble even after they lose? 
This is the only trick that I don’t use a clicker on. I just don’t think it’s necessary for Leroy and Jeannie because this was the first trick I taught them and they’re both very consistant with it.
If you do want to use a clicker, click when they’re a few steps away from you, as they’re running to you – don’t wait until they get there. Then when they get to you, give them the treat. If you use the clicker – never never never unpair the clicker from the treat! If you click, you must give them a treat. So when you get to the final stage and only treat sometimes, don’t click either. This is true for any trick.
Good luck!