When men and women share the same environment, they sleep with each other. Regardless of rules, policies or roles.

There are only two options, either A) to pretend that it doesn't happen, or B) to acknowledge that it does.

The idea that corporate policy could ever control what goes on people's bedrooms is of course absurd, that's just option A.

The point is not to prevent it, the point is to minimise the resulting liability. Whether by re-org'ing so that the people who are sleeping together are not in a direct reporting relationship, or by letting one party go, and so on...