Other than actually activating your core (and shooting for intensity over duration), the key to making planks not suck is to keep your mind busy, whether that's lifting limbs, walking around, or moving weights.
This exercise will hammer the trunk when you maintain a rigid plank. And once you've got that down, you can raise the difficulty by increasing the load or moving the weight in front of the hands.
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Tip: The Leaning Lunge
A forward lean on lunges increases the recruitment of the glutes and hamstrings. The dumbbells should be on the side of the front foot in the bottom position.