Physical constraint - landscape and actor

I created a laser beam actor (laser beam + sparks + lava ball at the base). I want to constrain the movement of this actor to the plane of the landscape an fix the z axis movement. I know I need to create a physical constraint component, but where do I do this? I tried making 3 different constraints within the laser beam actor and making the constraint between each laser beam component and the Default Scene Root but this isn’t working. Any ideas? Thank you!