Some animals can't be made to 100% no matter what and that includes some ingame ones. This might help.
From DD: http://www.ztcdd.org/DD/index.php?topic=1779.0
Number of animals allowed per exhibit: 3-10 with 30 squares for each adult.
Exhibit size (for 3 adults): 90 grid squares
Terrain (for exhibit with 90 grid squares):
36 Gray Stone, 27 Grass, 27 Snow
Foliage (for exhibit with 90 grid squares):
No foliage should be used.
Rocks (for exhibit with 90 grid squares):
14 Small Snowy Rock - Small, which is its most liked rock.
Elevation: Of the 90 squares, 2 nonadjacent squares should be elevated.