Now, to find the proper height of the fence at each point, all we need to do is determine the distance of that point to the origin, and find the height of the ball at the time when the ball has traveled that distance with this initial velocity. For instance, at the (baseline) end of right field,

Input := 

s4 = Solve[horiz[t]==425,t]

Output =

{{t -> 3.30457}}

Input := 

vert[s4[[1,1,2]]] //N

Output =

26.4574

So the fence should be about 26.5 feet at the right field end.

Input := 

s5 = Solve[horiz[t]==325,t]

Output =

{{t -> 2.52703}}

Input := 

vert[s5[[1,1,2]]] //N

Output =

52.3761

Yowza! The fence should be over 52 feet high at the left field end! All of a sudden, Fenway doesn't look so lopsided.