Supernatural Defense assists with concentration.
Supernatural Defense stats that
At 7th level, you gain extra resilience against your prey's assaults on your mind and body. Whenever the target of your Slayer's Prey forces you to make a saving throw and whenever you make an ability check to escape that target's grapple, add 1d6 to your roll.
However, I can't find any other instances out side of the Monster Slayer that use the wording "forces you to make a saving throw" so we have to look elsewhere for an answer.
The rules for concentration state that
Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration. The DC equals 10 or half the damage you take, whichever number is higher. If you take damage from multiple sources, such as an arrow and a dragon's breath, you make a separate saving throw for each source of damage.
This draws a direct link between the concentration check, the damage, and the source.
We can safely say that a dragon's breath is the source of a Dexterity saving throw. Therefore, the dragon who exhaled that breath onto you, forced you to make that saving throw.
Given the rules for concentration, we can equally say that an arrow is the source of a Constitution saving throw. Therefore, the archer who shot you with that arrow, forced you to make that saving throw.
This can be generalized to just about any situation in which the target of your Slayer's Prey forces you to make a Constitution saving throw to maintain concentration.
Moreover, I think that this ruling is supported by Supernatural Defense's flavor. After all, the damage involved is certainly an assault on your body, while the attempt to break your concentration is an assault on your mind.