If you do not use `frontend_model` your html for two fields will look like this

    <tr id="row_you_dependency_field_id">
        <td class="label"><label for="you_dependency_field_id">Dependency Field</label></td>
        <td class="value">
            <select id="you_dependency_field_id" name="groups[general][fields][you_dependency_field_id][value]" class=" select">
                <option value="1">Yes</option>
                <option value="0" selected="selected">No</option>
            </select>
        </td>
    </tr>
    <tr id="row_your_dependent_field_id">
        <td class="label">
            <label for="your_dependent_field_id">Dependent Field</label>
        </td>
        <td class="value">
             <select id="your_dependent_field_id" name="groups[general][fields][your_dependent_field_id][value]" class=" select">
                 <option value="1">Yes</option>
                 <option value="0" selected="selected">No</option>
             </select>
        </td>
    </tr>

The javascript to show/hide dependent field will look like this

    new FormElementDependenceController({"your_dependent_field_id":{"you_dependency_field id":"1"}});

And show/hide will work fine because both ids are present in html.

But if you use `frontend_model` the value for the second field is rendered by your custom block `module/adminhtml_form_field_test` and does not contain id of the dependent field and javascript just does not know what to hide.

    <tr id="row_you_dependency_field_id">
        <td class="label"><label for="you_dependency_field_id">Dependency Field</label></td>
        <td class="value">
            <select id="you_dependency_field_id" name="groups[general][fields][you_dependency_field_id][value]" class=" select">
                <option value="1">Yes</option>
                <option value="0" selected="selected">No</option>
            </select>
        </td>
    </tr>
    <tr id="row_your_dependent_field_id">
        <td class="label">
            <label for="your_dependent_field_id">Dependent Field</label>
        </td>
        <td class="value">
             ...
             //The output of your frontend_model
             ...
        </td>
    </tr>

So go to _toHtml() method of `module/adminhtml_form_field_test` and wrap the output into `div` and specify id for it

    $fieldId = $this->getElement()->getId();

    //your html 
    <div id="field id here">
        //your frontend_model html
    </div>