I've done breath control with an inflatable mask - with breathing tubes that can be closed off. It was wierd and fun... and is easy to restore the air by letting go of the tube (Mistress simply pinched it with her fingers). I've also done it with a latex gloved hand and a pussy (as described above). Not sure which is better but they were all carried out safely and for not very long periods (though it feels longer when you are doing it).