Big54bob, there are several people on this site, and thousands of people across the 'net who keep mantis shrimp safely in aquariums. They need to be kept in tanks pretty much by themselves since they will kill and eat other tank inhabitants when they get large.
That doesn't mean they can't be kept, it means they can't be kept with other creatures.
They are very pretty shrimp, with lots of personality, and generally well worth the effort of keeping.
Please do not post such strong advice if you are unfamiliar with the topic being discussed.
~JW