[@ReusableSword] - It depends on what is used to maintain them. A basic entrance only really needs attention should something block it's way or should the frame get damaged. If there's any sort of effects or enchantments imbued upon the entrance then they'll require a god to regularly recharge their divine magic or the magic behind their effects will wear away until the entrances revert to normal. Unless you're proposing that these crabs act as conduits for Naswaru's divine power to recharge whatever effects you might have had placed on the entrances then all that's needed is to check for mundane wear and tear amongst other things every so often.

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On a separate topic, just to clear up something for everyone just in case there was any confusion, deity's are the only sources of magic in this world. There is no generalized "Magic" in this world that isn't the direct result of some god or goddess lending their power. The only other force in this world is unseen and unknown to all currently.