Duck pecking order

[Lisa0169]

I am looking some advice. I had 2 drake khaki Campbells that I raised from ducklings. Unfortunately a predator got one. So I decided to get 2 hens for my drake so he wouldn't be alone. I got one Campbell and one rouen. The problem I am having is the 2 hens like to be next to each other all the time. This is not a problem when they are outside of the ponds. The problem comes in when they get into the ponds and want to remain next to each other. My drake chases the rouen out constantly. I don't know what to do with him. When they are out of the water there doesn't seem to really be an issue. The 2 hens follow him wherever he goes it's just in the water that he will not allow both of them in together. Any advice would be appreciated.