capturing deadlock property 24/7
SELECT XEvent.query('(event/data/value/deadlock)[1]') AS DeadlockGraph
FROM ( SELECT XEvent.query('.') AS XEvent
FROM ( SELECT CAST(target_data AS XML) AS TargetData
FROM sys.dm_xe_session_targets st
JOIN sys.dm_xe_sessions s
ON s.address = st.event_session_address
WHERE s.name = 'system_health'
AND st.target_name = 'ring_buffer'
) AS Data
CROSS APPLY
TargetData.nodes
('RingBufferTarget/event[@name="xml_deadlock_report"]')
AS XEventData ( XEvent )
) AS src;