Currently there are two types that exist as far as i know. Feel free to correct me.
There's Peggy's footstep mod that lets you set paint colors to footstep sounds so all you do is color the surface they are walking on to a particular color.
This is good, but the only problem is if you have two different "materials" that are the same color, then you can only stick with one color for each material.
The second is by Mr.Nobody and Port and it lets you set footprints via events. However, its for each individual brick you walk on and not on the player. Therefore, it becomes a hassle to put an event on every brick that is small if you have a ton of rubble or debris.
These were just alternate suggestions for you if you didn't know about them.
I believe that the mod Planr is describing would be like a better version of the second one described. Instead of eventing every brick to change the player's footstep, it would be one brick to toggle the player's footsteps to another sound.
Someone needs to get on this idea because the current footstep mods i know of do get the job done, but i don't think anybody has the patience to work with the restrictions that they have.