  We report a substantially simplified procedure, based on group-theoretic
reasoning, for the reduction of qubit leakage in exchange-only spin qubits. We
to find exchange sequences which accomplish leakage reduction with only two
additional spins and with as few as 14 nearest neighbor exchange interactions,
less than half than previously reported. We show that the identified sequences
are robust in the presence of realistic noise levels in the semiconductor
environment. Our procedure also produces flag information that can be helpful
in the implementation of quantum algorithms.
