I’ve been using Epoxy Putty for about 30 years now with great success. It comes in a long tube. The putty is dark grey with a white center. Kneed the two until it is a uniform color and simply put your wires inside. It is available at Home Depot and Lowes in the plumbing department.
Clear two part liquid epoxy also works. But, if you use this type make sure you sprinkle a little stone dust to discolor the clear expoxy, it looks much better. This type runs and is not as good or as easy as the putty type.
By the way I would NOT recommend using steel wire because it might rust and the planting would lift off the rock. I use copper wire, but have seen aluminum wire work just as well.
Good luck!