Melt the butter in a large skillet over medium heat. Stir in the garlic and onion and cook until the onion is soft and translucent, about 5 minutes. Stir in the shrimp and cook till they are bright pink on the outside and are no longer transparent in the center, about another 5 minutes. Drain and set aside.
In a large bowl, combine cream cheese with cheddar, shrimp mixture, half the bacon, half the pecans, and half the chives. Season with salt and pepper and stir until combined.
Empty bowl out onto a piece of plastic wrap and form into a ball or a log shape with your hands. Place in the refrigerator to harden slightly.
On a large plate, combine the remaining chives, bacon, and pecans. Stir so that they are evenly distributed on the plate. Remove cheese ball or log from refrigerator and roll in mixture, pressing more toppings on with your hands if needed. Place on a serving dish with crackers or vegetables for dipping.