In a large pot, fill it with fresh water and add the lemons, onions, potatoes, and garlic.
Bring the water to a boil.
Once boiling, add the shrimp and cook them 45 seconds or until they begin to peel easily from their shells.
After the shrimp are cooked, kill the boil with frozen corn and ice. Drain most of the water or take them out of the pot.
Prepare a Cajun seasoning mix and sprinkle it over the cooling shrimp.
Let the shrimp marinate in the seasoning for about 20-25 minutes, tasting occasionally to ensure it's not over-seasoned.
Serve the seasoned shrimp alongside crackers and a dipping sauce.
