How to handle Belongs To User relationship
Assuming your plugin is going to be the only thing referencing this Active Record relationship, your plugin could have its own MyUserRecord that extends Craft's UserRecord and does something like:

public function defineRelations()
{
    $relations = parent::defineRelations();

    $relations['myUser'] = array(static::BELONGS_TO, 'MyUserRecord', 'id', 'required' =&gt; true, 'onDelete' =&gt; static::CASCADE);

    return $relations;
}


And you would just utilize MyUserRecord instead of Craft's UserRecord in your plugin.