The word "foxcase" is relatively uncommon, which can make finding synonyms a bit of a challenge. However, there are a few words that could be used interchangeably depending on the context. For example, "foxhole" is a common military term that refers to a defensive position dug into the ground. In a less literal sense, "hideout" or "den" could be used to describe a place where a person or animal seeks shelter or safety. "Nest" could also be used to describe a similar type of structure. Lastly, "lair" is a more sinister synonym that could be used to describe a place where someone or something tends to hide or reside.