need advice: newly adopted cat, litter box use problems

My mother just adopted an adult, neutered male, declawed all 4 paws from the shelter yesterday. He is very sweet and loving and got on all our laps, explored, a real sweetie. Then he got in the litter box (yeah) but uh-oh, instead of squatting, he stood there and did the spraying thing with the urine stream going horizontal (and everywhere).

Yikes. Does that mean he was neutered "too late" and had already developed tomcat habits? I'm assuming there is no "training" him to squat. We have a male (and a female) cat that was neutered at 6 months. The only time he's ever sprayed was when we tried to introduce a 3rd cat to the household.

Any thoughts or advice would be appreciated. He seems perfect behavior-wise but this is unacceptable I'm afraid. We did put a box around the LB with the front open and thought we could get a covered LB and see if that would work.

Thanks!