Use of Golang reflection and DRYing out some code

I have a function that needs to receive a type, determine the subtype, then create a copy of the subtype. I keep staring at this function and I feel this can be simplified, but I just can't figure out how to get it functioning. Here's the code:

func AddProp(prop prop, x, y int) []prop {

  v := reflect.ValueOf(prop)
  fmt.Printf("Prop type is %v", v.Type())

  switch v.Type() {
  case reflect.TypeOf(&Fence{}):
      f := Fence{}
      f.New(x, y)
      props = append(props, &f)
  case reflect.TypeOf(&Rock{}):
      f := Rock{}
      f.New(x, y)
      props = append(props, &f)
  }
  return props
}

It's actually quite a bit longer than this with many more cases. Thank you for taking a look!