We summer on a large lake, complete with waterfowl. Our miniature schnauzer likes nothing more than rolling in goose poop, and she abhors almost nothing more than baths.  Can aversion training overcome instinct in this case?

This is a common problem. Dogs’ sense of smell is their primary source of information about the world — and one of their main pleasures is covering themselves in delightful scents. Unfortunately, we tend to disagree with their taste!

This is a natural dog behavior and very difficult to train away. A few suggestions:

Manage the environment: This means curbing your dog’s freedom, at least for a while. Only let her run free when you can keep an eye on her and stay close enough to intervene immediately if she heads toward the poop. No chances to roll in poop equals fewer baths and less frustration.

Work on a solid recall: Initially, do this inside, away from enticing distractions. Slowly work up to calling her to you outside, when she’s off leash. Always use a high-value reward (something she absolutely loves and gets at no other times). Whenever you are outdoors with her, have some treats with you. Practice, with her on leash, calling her toward you when she notices the poop. Lavishly praise and generously reward when she looks at or comes to you (remember, she’s on leash) when there is poop nearby.

Build associations: If you can ever catch her in the act, immediately tell her No! and bathe her or give her a thorough rinsing with the garden hose. If you never catch her in the act, bathe her the instant you see her covered in poop. (Be careful, though. This could simply cause her to be more sneaky about doing it.)
Build strong positive associations with not rolling in poop. When you are outside together, praise and reward her for coming when called, for ignoring poop, for any behavior you like, even if means you randomly go up to her, praise her, and offer her a treat for lying on the grass and being her beautiful self.

It’s doubtful that you will cure her completely of this charming behavior, but you might be able to make it less appealing.