"The enemy has a shield."
Translation:Hostis scutum habet.
"Hostī est scūtum" (dative of possession) looks fine to me. Did you report it, using the "report" function?
For the perplexed,
Use the dative of possession if you want to emphasize the fact of possession, rather than the possessor or the possessed:
There's a great passage in Caesar, where he describes the siege (by the Gallic tribe called the Nerviī) of the Roman camp led by Quintus Cicero (the orator's brother). He brings one event in that siege vividly to life by depicting the day that two rivals among the Romans ( = inimīcī, "not" (in-) "friends" (amīcī)) ventured forth outside the camp fortifications to attack the enemy ( = hostēs, the Gauls). Their names are Pullō and Vorēnus--one of my students knew that those names were used in the Roma TV series (I'm told they are also used in Colleen McCullough's novels about Caesar)--and they were real people.
Caesar describes them as rival centurions, who contended with each other, year after year, for who would get promoted first. (That's what makes each an inimīcus of the other.) The part that makes the story so great is that each rival, in turn, is needed to rescue the other from a group of hostēs that would otherwise have killed him.