Dogs always do things for a reason.
For example: the dog is scared or anxious about something, in pain, tired, hungry, bored and so on.
A qualified dog trainer/behaviourist:
Will diagnose the reason and address it with change in logistics or management combined with training.
An unqualified person will:
Tighten the lead
Use a slip lead or choker
Intimidate the dog
Poke it's ribs
Pin it down
Tell you it's being dominant
Back it into a corner
Electrocute it.
Feel free to add some more if you have experienced this.