My Dad had a cast on his arm, and found it difficult to do bodywork -
the weight of the cast along with holding the hammering dolly... He
eventually used the cast as the dolly - held it up under the metal while
he hammered on top. After a while the cast was beaten to a pulp so Dad
mixed up a batch of PolyFilla and repaired it. The technician in charge
of removing the cast several weeks later had a helluva time cutting
through that Poly!