Unpublish node based on field option Is there a way to unpublish a node if a user selects an option from a select list in field?

I have a field that has a list of cities. What I would like is if the user selects a certain city like London for example, the node is automatically unpublished so it can be moderated.

I have been trying with rules but every time I test my rule nothing happens so I'm sure there is something wrong with my rule or maybe there is an easier approach?
You could also hook on hook_node_presave() and check here the value of the field... No ?

mymodule_node_presave($node) {
if($node-&gt;yourfield[.....]['value'] == 'London') {
$node-&gt;state = '0';
}
}