  We measure changes in the penetration depth $\lambda$ of the $T_c \approx 6$
K superconductor LaFePO. In the process scanning SQUID susceptometry is
demonstrated as a technique for accurately measuring {\it local}
temperature-dependent changes in $\lambda$, making it ideal for studying early
or difficult-to-grow materials. $\lambda$ of LaFePO is found to vary linearly
with temperature from 0.36 to $\sim$2 K, with a slope of 143$\pm$15 \AA/K,
suggesting line nodes in the superconducting order parameter. The linear
dependence up to $\sim T_c/3$ is similar to the cuprate superconductors,
indicating well-developed nodes.
