Minecraft Earth Powers

I'm doing some command blocks to make earth powers in Minecraft, the first step for me is this command

/scoreboard objective add Earthling

Simple, Now I have an old answer for an assassin kit I did once, but it doesn't work when I swap it over. This is the command I want to work after it finds out who has the Earthling tag

/execute @a[tag=Earthling] ~ ~ ~ detect ~ ~-1 ~ air 0 /setblock ~ ~ ~ grass

Also, you must be wearing boots to make this work, here is what the guy who answered my assassin kit problem to do. If you can convert this to 1.12 command block logic for me so it will sense I have leather boots on I would be very happy.

Solution 1:

You will just need to add quotes around the

minecraft:leather_boots

so it is:

"minecraft:leather_boots"