How would they get in? From neighbours places under the fences?
Foxes love urban areas - they are happy to look through garbage bins. The place I have seen the most foxes is Central London lol. The fox that ate our chooks came under a fence via our neighbour's yard. We were on holidays and the guy who was feeding them hadn't put them in the coop for the night. If the hens have a safe place for the night they should be ok. Foxes aren't brazen enough for daylight attacks they usually sneak in overnight.

ETA - if you're going to a poultry auction try to buy young chooks because older hens lay less eggs.