execute as @e[type=marker,tag=flag_dropoff] at @s unless block ~ ~-1 ~ minecraft:gold_block run kill @s

execute as @e[type=marker,tag=aqua_flag_location] at @s unless block ~ ~-1 ~ minecraft:light_blue_concrete run kill @s
execute as @e[type=marker,tag=light_purple_flag_location] at @s unless block ~ ~-1 ~ minecraft:magenta_concrete run kill @s
execute as @e[type=marker,tag=green_flag_location] at @s unless block ~ ~-1 ~ minecraft:lime_concrete run kill @s
execute as @e[type=marker,tag=yellow_flag_location] at @s unless block ~ ~-1 ~ minecraft:yellow_concrete run kill @s