Grave marker help!

Hello,

My great-great-great-grandfather was Michael Rooney, lived 1821-1903 in Lisheenkyle, Aughrim, Co. Galway for some time, but most of his life was spent as a farmer in Rahard, Athenry. He died in Castlelambert in April 1903 at the age of 76. From there, the records cease to exist. After digging, we've discovered that at least one of his three sons, Martin, also lived in Athenry at some time. Records get a bit muddy because they farmed in different areas than they lived. But we believe we have found his grave marker, which serves as a mass grave for several of his family members. Here is the link for the grave: http://irishgraveyards.ie/plot.php?plotno=242&yardid=103&section=B. 

But Michael Rooney is not listed among those buried there. We've been searching in archives, church records and every other place we can think of, but he and his wife, Margaret Rooney (nee Connolley, 1835-1895) are nowhere to be found. Does anyone have access to the Athenry Graveyard and willing to see if those two are nearby? Or does anyone have any information on burials in the late 1800s? We wonder if they were buried on their land perhaps. Any help is much appreciated!