@windmill what brand of tire liner were you using? Most liners have a smooth or tapered end that would face down next to the tube to prevent cuts. We also trim down liners to fit smaller tires and use a curved or rounded cut on the ends to prevent pinching that a straight cut might cause. Mr. Tuffy's, Stop Flats2, and RhinoDillos all seem to work well.
The extra protection with the Schwalbe Marathon Plus & Big Ben Plus tires is good; however, it's still a good idea to use a tire liner in addition, especially if you have a rear hub motor wheel. Not a lot of fun to fix a flat on one of those on the road! There are
Fat Bike tire liners by Mr. Tuffy; a bit pricy but they make them for 3-4 inch wide tires and 4-5 inch wide fat tires.