Man, I am so very sorry to hear that. A theft is a theft, and no one should have to go through that, but I don't think I'd put your plants out front of the house anymore after this. If you really have no room for them in the back, you may want to invest in a driveway alarm such as this: (
Amazon link). You can set up one or more sensors per system, and the receiver will beep inside if anyone approaches within 9 meters (just over 27 feet) of one. They're solar powered too, so no worries about batteries dying. They wouldn't prevent a theft if you're not home, but at night at least you'd know if someone was near your trees.
My outside potted plants, the most expensive of which is only worth $100, are currently in our 6 foot fenced in back yard. I'm not all that concerned with theft at the moment, but when I start building up a collection with trees that are worth several hundred dollars or more apiece, then an outdoor alarm system such as the one above will definitely be put in place, in addition to Wi-Fi cameras around the yard. For the price of one $500 tree, you can set up a pretty decent DIY alarm system.
For insurance purposes, I also recommend having your most expensive trees appraised by a professional to document their value.