Stealth Rock on LO Mamoswine isn't terrible, but every time I used it I wished I had a more reliable user like Heatran or Deoxys-D. Hell, I'd even lean more toward using Focus Sash Dugtrio for Stealth Rock. Additionally, I personally found that Mamoswine gets very few opportunities to set up Stealth Rock. It's not nearly as frail as Pokemon like Lucario, but it isn't really bulky and has few resistances; factoring in Thick Fat, it only has three resistances, one of which is worthless (Poison). On top of that, most of the Pokemon it forces out are either 4x weak to Ice or both slower than it AND weak to one of its moves, of which there aren't many.
That said, I do think it's good enough for an AC mention for when the Mamoswine user really can't fit on any other Stealth Rock user.
EDIT: Also, I agree with Scarfwynaut (wow! what are the odds?) that CB should get an OO mention, but definitely stress the fact that its moves are by no means safe to be locked into.
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman
I am not lucaroark on Pokemon Showdown.
I'm always on PS as Adamant Zoroark.