ants have colony outside

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i have this HUGE ant problem outside, i've been trying all sorts of over the counter pestiside ant killers but nothing seems to be helping. Now i've been reserching on the net and it looks like im going to have to order a product that is bait then kills them. There colony is a gravel hill where a stump use to be i think, and its approximitly 2x2 section what would the ideal thing to use be Thank You