Coil problem on miller cycle mazda millinia 01

Have replaced 3 coils on front of engine,they all failed at different times but after fixing #6 coil car ran fine for a day and noww #1 is not working. Checked plug and am pretty sure its another coil (170bucks plus tax) if # 3 and #5 fail it will be a tuff task. Is there any way of preventing? Spent alot of money over a yr ago and had all plugs changed,water pump,coil and misc. others (over 2k). Any help is appreciated