Our place is in Florida with river and gulf access and we are constantly asked if we have kayaks and canoes. We do but do NOT allow guests to use them. Looking into this extensively and speaking to the underwriter of our homeowners policy there is no liability protection once the kayak leave the property.
As the underwriter explained it to me... If a guest were sitting in a kayak in your driveway and fell over and hit their head on the concrete and died, you're covered. If a guest takes the kayak to a nearby body of water, tips over and hits their head and drowns, you're totally liable.
This also includes bikes. Use the same logic above. Once guests leave the property with your bikes, kayaks and canoes, it's on you.
Yep, it's frustrating seeing other "competitors" in the area offer these amenities and lure bookings away from us. Also, Airbnb should remove these items from the amenities options for owners. Having these options there implies that they are in the same liability category as say... a toaster oven.
Solution: We keep our Airbnb area guide up to date with rental options for kayaks and bikes. It works and most importantly the liability is shifted to the guest and the rental company.
Believe me, I would be more than pleased to hear I'm totally wrong here and there is a solution. If so, please post so I can learn more.