As far as we know there is no single crystal neutron study on ErPr_2Si_2 yet, mainly due to fabrication difficulties. We have grown large (diameter: 6 mm; length: 8 mm) single crystals at 120 atm. Comprehensive in-house Laue, XRD, PPMS and SQUID characterizations show that spin fluctuations, short- and long- range antiferromagnetism exist at different temperature regimes. Present magnetic models reported from powder diffraction are controversial. We thus propose a combined time-of-flight neutron Laue diffraction study to reveal the nature of these intriguing properties. This study will unambiguously determine: (1) The long-range AFM structures below 2.5 K and between 2.5-3.8 K. (2) The 2D/short-range AFM structure between 3.8-4.8 K. (3) The spin fluctuations between 8-30 K. (4) The interplay between these phases. This compound is unique in combing these intriguing physics in one sample.