It is a continuous battle to keep the ants out of the dog's food bowl.
According to Popular Mechanics magazine the best way is to spray a ring of Q20 lubricant spray around the bowl and the ants will stay away. Definitely worth a try.
Another solution I came across is drawing a circle around the bowl using a bar of soap, go over it a few times to make it nice and thick - the ants seem to stay away from the soap.
Another solution is using two bowls, one with a larger base than the other and put the dog's bowl inside the bigger bowl and fill the bottom of the bigger bowl with water - you need to somehow keep the dog's bowl from moving too close to the edge of the bigger bowl, which gives the ants a bridge to "attack".