Table schema:
CREATE TABLE table_name_28 (venue VARCHAR, competition VARCHAR, position VARCHAR, year VARCHAR, notes VARCHAR)

Question: Which venue did the African Championships have after 2006 with a position of 2nd and 3000 m s'chase in notes?
SQL: SELECT venue FROM table_name_28 WHERE year > 2006 AND notes = "3000 m s'chase" AND position = "2nd" AND competition = "african championships"