first by a mine so when you hit it, it blows most of the turtles up earning up to 400-500 combo each time. do that about 7 times. next buy some buzzsaws to bounce the turtles earning up to 700-900 combo each time. now install some turrets to shoot them earning up to 1000-1200 so you can buy more mines and buzzsaws. now add some flow to make the turtles come out a bit faster.keep hitting the mines when the turtles come and you will be getting up to 2000-3000 combo points. now add some lasers to blow the turtles up and you will be get up to 5000-6000 combo points each time.