like (the) white on rice
Extremely close; as close as possible. If that forward tries to get in our zone, I'll be on him like white on rice! You better pass this test, or else I'll be on you like the white on rice for the rest of the semester to make sure you're doing homework.
like the white on rice
and as the white on rice phr. as close as anything can be. Those two are really close—like the white on rice.