In PT3, you can configure your HUD to only show the last X number of hands. In the "Hud Options" tab of your configuration screen, set a positive number in the "Stats from the last [ ] hands" box.

Also, I've gotten into the habit of occasionally checking a player's session stats (in PT3, the per-session data will pop up if you hover over a specific stat long enough) if I think they have changed their strategy. Every once in a while I'll find a nit-turned-lag, or fish-turned-tag, etc. Obviously, that's only really useful for VPIP and PFR, since other stats take longer to converge, but at least you'll have an idea if he's playing differently than you expect.