  The magnetoresistance of iron pnictide superconductors is often dominated by
electron-electron correlations and deviates from the H$^2$ or saturating
behaviors expected for uncorrelated metals. Contrary to similar Fe-based
pnictide systems, the superconductor LaRu$_2$P$_2$ (T$_c$ = 4 K) shows no
enhancement of electron-electron correlations. Here we report a non-saturating
magnetoresistance deviating from the H$^2$ or saturating behaviors in
LaRu$_2$P$_2$. We have grown and characterized high quality single crystals of
LaRu$_2$P$_2$ and measured a magnetoresistance following H$^{1.3}$ up to 22 T.
We discuss our result by comparing the bandstructure of LaRu$_2$P$_2$ with Fe
based pnictide superconductors. The different orbital structures of Fe and Ru
leads to a 3D Fermi surface with negligible bandwidth renormalization in
LaRu$_2$P$_2$, that contains a large open sheet over the whole Brillouin zone.
We show that the large magnetoresistance in LaRu$_2$P$_2$ is unrelated to the
one obtained in materials with strong electron-electron correlations and that
it is compatible instead with conduction due to open orbits on the rather
complex Fermi surface structure of LaRu$_2$P$_2$.
