Use in more than one city

Just add a taxonomy to deal with your pet posts:

<?php
add_action( 'init', 'create_state_tax' );

function create_state_tax() {
	register_taxonomy(
		'state',
		'pet',
		array(
			'label' => __( 'State' ),
			'rewrite' => array( 'slug' => 'state' ),
			'hierarchical' => true,
		)
	);
}
?>

More https://codex.www.ads-software.com/Function_Reference/register_taxonomy

Hi Diana, nice plugin!!! congratulations

Please can you tell me please where must I insert this code?

Thanks
Regards
Juan

You can insert in theme functions.php or create a plugin (it is just a file just some specific header see https://codex.www.ads-software.com/Writing_a_Plugin).