It simply means to 'Prevent some harm coming to us or ourselves'. Firstly, in decent English usage, the word 'ass' can also mean a 'donkey'. But, I assume the meaning of 'ass' in this context is 'butt', or the 'backside'. It's indecent to use it unless with close friends. Similarly, when something wrong happens to us it is said that 'our ass got kicked'. Another related phrase is 'I'm going kick his ass' (I'm gonna beat him or he will lose to me). Cheers.

my ass = me; your ass = you; our ass = us; etc. It can be used just about anywhere.

It simply means, "save us". The writer used "our ass" ("our collective ass"?) because it's slightly crass, and therefore gives a stronger effect to the plea. Because the phrase is still impolite to say, it's better to avoid using this.

it means "save our self" cowboy...