Wiktionary
inground
a. inside the ground
Usage examples of "inground".
There was nothing left but the grind of the chaser's propellers, and then an abrupt metallic whistle, which came in staccato bursts for perhaps ninety seconds, Fortunately for the sanity of all hands, Sparks had his wits about him, or had his training so inground in him that he didn't need wits.