No lifeguard is on duty: swim 'at your own peril'. [='at your own risk']
The species is 'in peril' [=(more commonly) 'in danger'] of dying out.
Restaurants that ignore the smoking ban do so 'at their peril'.
(..) Human beings venture into the highest parts of our planet at their peril. Some might think that by climbing a great mountain they have somehow conquered it, but we can only be visitors here. This is a frozen alien world. This is the other extreme - one of the lowest hottest places on Earth. (..)2006 TvShow: Planet Earth Title: Mountains Season: 1 Episode 2