The phrase "chained dogs" refers to dogs that are kept tied up with a chain. It often implies that the dogs are not able to roam freely or move around as they are restrained by their chains.
Sentences with «chained dogs»
It is cruel to chain a dog outside to a post. (cspca.com)
You may opt to get choke chain or spike chain dog training collars. (dogobediencenet.com)
If all you want to do is chain a dog outside, don't get one. (dogingtonpost.com)