I have five dogs (mostly failed fosters) and a foster puppy. I trust their judgment. My ex sister in law brought her new boyfriend to the house and my dog wouldn't let him come in. My sister in law met the guy in court ordered drug rehab right after he was paroled. A month after he came to my house the guy drugged my sister in law and stole her car. He had his own car, but he was going to make a drug buy and didn't want to loose his own car if he got caught. Our dog had never been that aggressive with anyone before or since. He just hated that guy.
