In the wild, take them down with Wyvern breaths or leave them alone.

If one of those is employed by enemies, make use of Compound Bows or Velonassaurs in case getting near isn't a possibility.

If you absolutely need to bite those things, use a Reaper King, as they reduce any source of damage - aside poisonous breaths - when not affected by light, including damage reflected by Arthropleuras and Kentrosaurus. Remember, damage reflection ignores saddles.

More Kentrosaurus Encountering Tips