How to keep a humanoid from taking damage?

In my game I want no chance that players can take damage, but I don't want to use forcefields. Is there a different way to keep the humanoid from taking damage? I tried using

Humanoid:GetPropertyChangedSignal("Health")

and updating it every time it's not at 100 but nothing happens. Neither does looping and checking if it's at 100.

Hey. Try this:

local Humanoid = script.Parent.Humanoid

Humanoid.Changed:Connect(function(property)
    if tostring(property) == "Health" then

       local maxHealth = 100

       Humanoid.Health = tonumber(maxHealth)
   end
end)