Heated exchange with neighbors (warning long story)

So about two months ago, I had a couple in their late 50s-early 60s from Virginia move in next to me. When they first moved in, I was doing some yard work and saw the husband outside moving boxes into his house. So I did as any good neighbor should, walked over, introduced myself, and offered to help. He gave me a limp sort of disinterested hand shake and told me that he could handle it on his own. Anyway, they have this big Newfoundland dog who they have repeatedly let take a crap in my front yard multiple times every week. I finally got fed up with it about a month ago and walked over to ask them to please, at least pick it up with a shovel if they were gonna let him go in my yard. The wife then acted all offended and gave me the whole “My dog would never do such a thing” spiel and threw it all back on me. Fast forward to Sunday evening, I threw a party at my house for the football games, and I looked out the window to catch the damn dog red handed in the act of taking a monstrous dump right in the middle of my yard. I told my friends the whole story, and they came up with the brilliant idea to give my inconsiderate neighbors a taste of their own medicine. We ended up taking the pile of shite, putting it in a Rouse’s grocery bag, and dropping it through their mailslot right back into their house while they were out to eat. Welk, the neighbors proceed to call the police because apparently they stepped right in it when they opened their front door when they returned home. I was told that I will be fined if I commit another such action and run the risk of being arrested for vandalism. Were my friends and I justified for our actions?