$this->request->get() doesn't work inside FormRequest

The following form request is what I am attempting to create. It throws an invalid argument supplied for foreach error.

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class SaveCatRequest extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        $rules = [
          'age' => 'required|string|in:cub,adolescent,adult',
          'gender' => 'required|string|in:male,female',
          'species' => 'required|numeric',
          'pelt' => 'required|numeric',
          'nose' => 'required|numeric',
          'mane' => 'required|numeric',
          'pawpad' => 'required|numeric',
          'eye' => 'required|numeric'
      ];
    $markings = [];
        foreach ($this->request->get('m') as $m) {
            $mark = explode(",", $m);
            array_push($markings, (object) ['name' => $mark[0], 'color' => $mark[1], 'opacity' => floatval($mark[2])/100.0]);
            foreach ($markings as $key => $val) {
                $rules .= [
                    'name.*' => 'required|exists:markings',
                    'color.*' => 'required|exists:marking_colors,name',
                    'opacity' => 'required|between:0,100'
                ];
            }
        }
        return $rules;
    }
}

What am I doing wrong here?