If you are getting reinfected with the same or similar threats repeatedly then the root vulnerability that let in the hack the first time is still there.
If this hack is coming in through a server vulnerability or from another infected site on the same server then there is no plugin that you can put on this site that will stop it for good. You need to find the root cause, the source of the infection.
Is this a shared hosting account?
If so, how many sites do you have on your account?