I use a good asian fish sauce in beef stews (and chili, or cuban-style picadillo, etc) -- nobody notices any fishy taste, it just bumps up the umami and "beefiness"!
Following Kenji Lopez-Alt, I’ve put it in Bolognese sauce where it does surreptitiously add a bit of umami and body.
Marmite and Vegemite are also really good for adding some umami-saltiness to tomato sauces and stews without being very noticeable for what they are. (Assuming I can stop myself from spreading it all on toast first...)