Put Transactions in the Controller or Model

[eluser]asciiCode[/eluser]
I have been reviewing my code and noticed that I am placing a lot of business logic in the model.

The reason for this is because I believe the database transactions have to be called in the model? Is this true or can I start a database transaction in the controller so it looks something like this in the controller

$this->db->trans_start();
$this->my_model->InsertSomeInfo();
$this->my_model->DeleteSomeInfo();
$this->db->trans_complete();

Thanks!