why am i burning up number 4 plug in my 2000 expedition?

fords of this year have a huge problem of blowing out spark plugs since they used an aluminum black and only put 5 threads in it the best way is to get a thread insert put in this is usually done in a shop since it requires boring out the hole and then rethreading the whole thing since it keeps burning up the plugs it may be that either the plug or the insert that you have now is leaking exhaust gas and fouling the plug