I also carry a chapstick container, but it is filled with silicone grease. I apply just a small amount, right where the mask sits on my moustache.
I also find that combing so that all the hairs are pointing in the same direction makes getting a seal easier. On a few dives where I was having leakage problems, just a little grooming/combing of the moustache with the side of my finger stopped the leaking. The silicone grease or chapstick also helps to keep the stray hairs from making bumps that leak.
And when diving frequently, when showering I use lots of conditioner to keep the moustache smoother and more flexible. The mask doesn't seal as easily when my moustache has the rough, stiff, strawlike texture from long, repeated saltwater exposure.
I put my mask on well before entry, and then suck in hard through my nose a few times to seat it. This works better than slipping on the mask and then splashing in immediately.
When looking for a mask, consider frameless masks. They seem, for me at least, to seal better.
It also helps if you are tolerant of water in the mask. If it is leaking, I only clear it when it starts getting up near my eyes. Otherwise I'll wash out all of the defog early in the dive and will have to purposely flood my mask later in the dive to defog it.
Don't forget to clear before flipping upside down to look at a ledge. I forget way to often and do an unintended saline sinus rinse.
A flooded mask should be just a minor irritant, not a big panic inducing problem. Your husband really, really needs to be comfortable clearing his mask and breathing with no mask on.
Don't pull the mask strap too tight. Beyond a certain point, pulling the straps tighter actually causes more problems. OTOH, if the mask seals good when you are looking down, but leaks a lot when you roll over on your back and look straight up, then you need to tighten up another notch or so on the mask strap.