Explain how you got your last job.
I don't have a previous job. I work for the police since 18 years ago.
I don't have last job. I have been working in police for 18 years.
I'm not a last job. I work in a police there are 18 years.
Are you saying this?
I'm not unemployed. I have been working as a policeman for 18 years.
Not bad !