I have two Terriers mix. One is a Chiuaua rat terrier mix and the other is the daughter of my first, with Boston terrier and Jack terrier. At first they would sit and stare intently at the indoor pen we had when the ducks were little. Runky, my female, would sit and shake. She did this again when we started putting the ducks in thier pen during the day. I was very carefull to not have the dogs and ducks in the open together till they were like 3 months old. One day my son let the dogs out while I was allowing the ducks to free range. The dogs did nothing but sniff and back off. Plus it didn't help that I came charging at them like a freight train! lol
So a few weeks later I wanted to see what would happen if I allowed the ducks to be around the dogs. I let the ducks out and everything seemed fine. The dogs were very curious but under my strict watch and correction, I made them keep thier distance and said "No!" a lot even if they were just looking. So we started letting the ducks out in the yard, but ONLY if someone was out there to watch. After a while we started to see that the dogs and ducks were use to eachother and didn't bother eachother at all. I would watch from the sunroom and everything was fine. I would let them out and cook dinner while checking on them, all was still fine. Now I let my ducks out all day with the dogs and there have been no problems. We do however have to feed the dogs away from the ducks. The ducks will try to eat their dog food and the dogs are very defensive over their food dishes. So to keep tempers from flaring, we feed them in the sunroom where the ducks have no access. Snacks or treats are handled the same way, it has to be seperate. They can share water bowls but that's it!
If tempers do flare it has to be corrected right away.
For a while there when we first let the ducks out, they would run and throw themselves at the dogs. Not sure what they were doing but if the dogs got too close, they would get attacked by the ducks. So the dogs would avoid the ducks. They would be careful to walk way around the ducks to keep from getting railroaded by them. It was actually kinda funny to watch. The dogs would just sit there and take the abuse! lol
Now they kinda are like buddies. Sometimes we will find them all asleep under the same tree, or I have seen all of them resting on the hot tub cover. I have also seen the ducks run to see what the dogs are barking at in the back yard. They will run up behind the dogs and peer through the fence with them. They also come running with the dogs when we I call. In a sense it's like having 4 dogs.
I have been lucky so far, I know the risk and it could happen, but I think it also depends on the temperment of your dogs. You have to play it one step at a time to see how they will react.
I forgot to say...the dogs and the ducks are pretty much the same size of eachother, not sure if this has anything to do with it?