The entity builds a trail but the trail spawns infinite blocks in the air

Ok so i'm the creator of "Sherisal and Friends" and i need some help ! I made a new mob that has the apparence of a blob. I had an idea to make that the blob leaves a trail (a block in this case) it works but the problem is since the entity is on the ground it places the block but when it's in the air, the trail is placing infinite blocks and i don't know how to fix this.