How to restrict a locator to a line that changes based on manipulated variables?

I am trying to have a locator move along a manipulated line but every time I manipulate the variables the locator doesn’t move across the new line. How can I get the locator to move across the line even after I manipulate it? Also when I try to move the manipulator it just goes to the bottom of the graph and doesn’t work. I’m not really sure how tracking function is supposed to work so I know that’s why that part doesn’t work.

Here is my code:

Manipulate[
 Plot[
  1/(4 f) (x - h)^2 + k,
  {x, -16, 16},
  PlotRange -> {{-16, 16}, {-16, 16}},
  AspectRatio -> 1/1,
  Epilog ->
   {
    PointSize[.02],
    Line[{{h, k + f}, {z, 1/(4 f) (z - h)^2 + k}, {z, k - f}}],
    Point[{{h, k + f}, {z, 1/(4 f) (z - h)^2 + k}, {z, k - f}}],
    Dashed, InfiniteLine[{h, k - f}, {1, 0}]
    }
  ],
 {{p, {z, 1/(4 f) (z - h)^2 + k}}, Locator, 
  TrackingFunction -> (p = {First@#, 
        1/(4 f) (z - h)^2 + k@First@#}; &)},
 {{z, 0}, h - 16, h + 16},
 {{f, 1/4}, -8, 8},
 {{h, 0}, -16, 16},
 {{k, 0}, -16, 16}
 ]

f0[x_, f_, h_, k_] := 1/(4 f) (x - h)^2 + k

Manipulate[Plot[f0[x, f, h, k], {x, -16, 16}, 
  PlotRange -> {{-16, 16}, {-16, 16}}, AspectRatio -> 1/1, 
  Epilog -> {PointSize[.02], Thick, Line[{{h, k + f}, p, {z, k - f}}],
    Point[{{h, k + f}, p, {z, k - f}}], Dashed, Gray, 
    InfiniteLine[{h, k - f}, {1, 0}]}], 
 {{p, {z, 1/(4 f) (z - h)^2 + k}}, Locator, 
  TrackingFunction -> (p = {First@#, f0[First@#, f, h, k]}; &)}, 
 {{z,  0}, h - 16, h + 16, TrackingFunction -> (p = {#, f0[#, f, h, k]};
     z = #; &)},
 {{f, 1/4}, -8, 8, TrackingFunction -> (p = {First@p, f0[First@p, #, h, k]};
     f = #; &)}, 
 {{h, 0}, -16, 16, TrackingFunction -> (p = {First@p, f0[First@p, f, #, k]};
     h = #; &)}, 
{{k, 0}, -16, 16, TrackingFunction -> (p = {First@p, f0[First@p, f, h, #]};
     k = #; &)}]