One more thing about walking the pup. "Field walking".

Don't take any company with you. No older dog. No human. Keep your attention on the pup! Don't rush the pup. Don't try to make the walk a conditioning exercise for yourself.

The pup should grow up with being in the field with you a normal part (the best part!) of life.

When he focuses on a critter, bug, bird, mouse, or whatever, pause and allow him time to work it out.
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I was on the bank.