How long are you leaving them vacant?
Are they on the lots where they will be worked on and eventually sold or in a holding pen somewhere?
If you don't have a person that can be hired to be walking them daily and making sure they are all locked up, I would hire a security company to check them daily.
Make sure if they are in working order you leave lights on 24 / 7 inside and outside. If you have no power, I suggest a daily walk and security to keep an eye.