i don't believe in money pouches too. usually i stay safe by making myself a less appealing target. when i do carry a larger amount of cash, i stash it in a jacket pocket, underneath other clothes, in a dry sack, at the bottom of my backpack.
with a top loading backpack i then knot the closure (army bootlace style) with a proper knot at the end so that you have to unknot that first before pulling to release it. but that's just extra because you have to be pretty tall and have long arms to reach in when i'm standing cos it's a 65l backpack and the opening is around my neck even when not fully packed and before that, you need a find a way to remove everything on top of the dry sack first...
with a zippered backpack, i just use a locking carabiner to attach the zips together. my friend has a slighly better solution. he uses something like this to attach his zips together. without the 'lobster claw' of course. the one he is using needs a twist/pull to open and the mechanism is hidden, so it is not immediately obvious what to do. he passed me his backpack to try and i couldn't figure it out.
edit: there are some magnetic and screw types, his isn't. it's blardy cheap and light too.