My opinion only (easy to implement)...
Keep players "in initiative" for a few rounds after encounters (keep track of enemies bleeding out). During this time, does the player cast resistance? Does the player cast guidance?
Another suggestion (also easy to implement)...
Ask the order in which the spells are generally cast (i.e. resistance followed the next round by guidance). At the beginning of each combat, roll a d10 to see how many rounds are left on those spells. If you roll a "3", the guidance has three rounds left and the resistance has 2 rounds left. If you roll a "1", the guidance only has one round left, and at the beginning of the player's turn, the resistance expires.
If you follow that suggestion, there is a good chance the player will counter with casting those spells once every 5 rounds rather than once every 10 rounds... which isn't really a problem, but it potentially slows the party down twice as much. In this case, the player has 1d10+5 rounds left (one fewer for the first spell cast).
Final suggestion (this one takes it too far in my opinion) ...
You also might need to keep track of detect magic. Is this player using detect magic (or other "detect spells")? That takes time (three rounds per 60 foot cone). To completely scan in four directions while also taking the time to rebuff resistance and guidance, it might take 2 minutes.
