Approach grafting as a technique can be applied to bonsai trees either when needing to fill a few gaps in the surface footage, also known as nebari or when needing to increase branch density in the canopy of the tree.
In either case, once the graft is completed it is of paramount importance that there is no movement. There are several ways to prevent disturbing the graft but the easiest and quickest is to use tacks of some sort, which are then nailed into the tree.
These tacks, which I buy when I am in Japan are ideal for the purpose.
There are 50pc tacks in the dispenser container.