Hello, @Lily_Fazbear . . . the black line on the mat is not fool proof at all. Mine have also wandered past that line, but I have built an area that has high enough walls to keep him contained if he should decide to go wandering.
Here are some ideas you can look at for a means to contain him so that he does not go wandering (in case he is trying to find the kitchen for a midnight snack). 