You should immediately pursue all statutory relief that is available to you especially if your juvenile record is eligible for sealing. Are you POST-certified? There are any number of working police officers in CA with juvenile records, so it may be that your prior record is not the reason (or the only reason) for the difficulty. Order up a copy of your FBI NCIC report thru the FBI web-site and then sit down with an experienced CA criminal defense attorney to figure out a plan to rehab your record.
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Contact an experienced attorney or the public defender's office in the county where you received the juvenile adjudications. They should be able to assist you with an application to seal your juvenile record. You may also find some helpful information at your local law library, public library, legal bookstore, or this link: http://www.nolo.com/legal-encyclopedia/sealing-juvenile-court-records-32228.html