Place butter on counter for about an hour to soften.
Combine cajun seasoning, garlic and butter in a bowl. Place on plastic wrap and form into a log. Place in freezer to firm.
Preheat smoker / grill with charcoal to 250.
Rinse and dry the chickens. Cut lemons into quarters. Stuff lemon slices and rosemary inside the cavity of the chicken. Tie the legs together with kitchen twine.
Cut butter into 1/4" slices. Use 3 slices per chicken. Place 1 slice under the skin on top of both breasts. Take the remaining slice, cut in half and place under the skin near the legs.
Generously coat chickens with cajun seasoning.
Place on grill opposite of coals.
Add wood chips every 20 - 30 minutes to keep a consistent smoke.
Cook until the breast temperature reaches 165.
Remove from grill and let rest for 20 minutes
Carve. Serve. Eat.