Building on the excellent suggestions so far, I've always done the following:
1. Create a safe space for cats that has food, water, litter box (in a closet), toys, etc. The cat space should be comfortable *and* safe. Block the entry so that the cat can easily access its room (without jumping over a gate), but the dog cannot. Here's what the kind of gate system that I have; in my setup, the cat door is bungee corded open:
2. Teach a Leave It command, without the cats present, then generalize the command to objects and cats. It's a very useful, potentially life-saving, thing for the dog to know. You can train the basics in multiple daily 5 minute segments over the course of a say a week. Can't find my favorite video link, but this one will do for now: Teach Your Dog to Leave It
3. Crate the pup whenever you're not home, or, if home, preoccupied. Do that until you are absolutely certain
that the dog doesn't pose a threat to the cat.
Unless your pup has insane prey drive, teaching it to coexist with cats really isn't that hard. It takes clarity and consistency to drive the point home (i.e., the cats are MINE), but it can be done.
A final thought. Make sure that your expectations are realistic. We all want our animals to happily coexist, even becoming best buds. That's not always possible, however. For me, the bottomline has always been twofold: (1) You may NOT chase the cats or in any way assault them, including pawing them to death
, and (2) Staring is verboten