A secured creditor has a right to go take property from his debtor as long as his doing so would not breach the peace. UCC § 9-609.
Bringing a police officer along does not make it not a breach of the peace. It is actually evidence that you did expect it to be a breach of the peace, and the uniform probably makes it a breach of the peace. To use the police, repossess it by judicial process, not self-help.
If someone tells you to leave, you have to leave. To do otherwise would be to breach the peace.
Lying and trickery is fine.
A creditor has a limited license to enter his debtor's property to enter property and retrieve the collateral, even cutting chains to do so. You cannot enter someone's dwelling house and probably not their fenced backyard however.
Courts are mainly concerned about preventing violence.
A secured party may deduct attorney's fees and collection costs from the value of the collected property. UCC § 9-607.