data merge entity @s {drop_chances:{feet:0f,legs:0f,chest:0f,head:0f}}
execute store result score random itemcount run random value 1..4
execute if score random itemcount matches 1 run data modify entity @s drop_chances.feet set value 1
execute if score random itemcount matches 2 run data modify entity @s drop_chances.legs set value 1
execute if score random itemcount matches 3 run data modify entity @s drop_chances.chest set value 1
execute if score random itemcount matches 4 run data modify entity @s drop_chances.head set value 1
tag @s add dropfix