With a little determined effort, a kangaroo can clear an 8' (2.5M) high obstacle easily. You'd need deer-proof fences (10' or 3M high) to prevent kangaroo incursions onto runways and airstrips - and even then, there have been reports of kangaroos being chased, clearing 10' obstacles. Just one of the minor hazards of aviation and driving in Australia. There have been a number of reported roo-strikes by aircraft, particularly on landing, not so much on takeoff.
Kangaroo easily clears normal fence in his stride
Call for Kempsey airport perimeter fencing after Mooney strikes kangaroo on landing
RFDS turboprop taken out by kangaroo
ATSB - Aviation wildlife strike statistics, 2002-2011 (a total of 66 reported kangaroo strikes by aircraft in this period)