Whenever Peter reprimanded his children for a particular behavior, they would answer, "But you do it!" His answer to that is probably every parent's answer, every parent who has "smart alecks" (as Peter would say) for kids:
"Do as I say! Not as I do!" . . . an expression Peter probably picked up in the early 1920's when he first came to this country (although the expression can be traced as far back as the New Testament)!