how i supplement 'choose one' choice combobox selector following countenance cakephp?

i am cake php novice.

i wish correct list "issue". list contains domain "priority_id" associated another list called "priority" an unfamiliar key. list contains 3 values "severe", "disaster", "todo". user name priority controlling combobox (input select).

the priorities hallowed this:

$priorities = $this->issue->priority->find('list');

this works me.

i need supplement fourth choice combobox called "choose". value default one. user can't quarrel form value selected. proclivity force user name revealing values instead submitting initial randomly.

1) i fill array $priorities ?
2) i countenance form?

thanks