Overwriting magento grid class of custom module - php

Question

I have a custom module and this lists some records in the admin panel. Currently there is no link to the list of records and I want to give a custom link to the listing. I have tried to overwrite the grid block class. But this is not working.
Code is given below:
<config>
<global>
<blocks>
...
<adminhtml>
<rewrite>
<partners_grid>Tech_SecodaryProduct_Block_Adminhtml_Partners_Grid</partners_grid>
</rewrite>
</adminhtml>
...
</blocks>
</global>
I have created a file under local/Tech/SecodaryProduct/Block/Adminhtml/Partners/Grid.php
<?php
class Tech_SecodaryProduct_Block_Adminhtml_Partners_Grid extends Webkul_Marketplace_Block_Adminhtml_Partners_Grid
{
protected function _prepareColumns(){
// parent::__construct();
$this->addColumn('partnerstatus', array(
'header' => Mage::helper('customer')->__('Seller Status'),
'index' => 'partnerstatus',
));
$ispartnerEnabled = Mage::helper('core/data')->isModuleOutputEnabled('Webkul_Mppartnergroup');
if($ispartnerEnabled == 1){
$this->addColumn('group', array(
'header' => Mage::helper('customer')->__('Group'),
'index' => 'group',
));
}
$this->addColumn('order', array(
'header' => Mage::helper('customer')->__('Order'),
'index' => 'order',
'type' => 'text',
"filter" => false,
"sortable" => false
));
$isThisEnabled = Mage::helper('core/data')->isModuleOutputEnabled('Webkul_Sellerstatus');
if($isThisEnabled == 1){
$this->addColumn('sellerstatus', array(
'header' => Mage::helper('customer')->__('Seller Status'),
'type' => 'text',
'index' => 'sellerstatus',
"filter" => false,
"sortable" => false
));
}
$this->addColumn('Telephone', array(
'header' => Mage::helper('customer')->__('Telephone'),
'width' => '100',
'index' => 'billing_telephone',
));
$this->addColumn('billing_postcode', array(
'header' => Mage::helper('customer')->__('ZIP'),
'width' => '90',
'index' => 'billing_postcode',
));
$this->addColumn('billing_country_id', array(
'header' => Mage::helper('customer')->__('Country'),
'width' => '100',
'type' => 'country',
'index' => 'billing_country_id',
));
$this->addColumn('billing_region', array(
'header' => Mage::helper('customer')->__('State/Province'),
'width' => '100',
'index' => 'billing_region',
));
$this->addColumn('customer_since', array(
'header' => Mage::helper('customer')->__('Seller Since'),
'type' => 'datetime',
'align' => 'center',
'index' => 'created_at',
'gmtoffset' => true,
));
if (!Mage::app()->isSingleStoreMode()) {
$this->addColumn('website_id', array(
'header' => Mage::helper('customer')->__('Website'),
'align' => 'center',
'width' => '80px',
'type' => 'options',
'options' => Mage::getSingleton('adminhtml/system_store')->getWebsiteOptionHash(true),
'index' => 'website_id',
));
}
$this->addColumn('deny', array(
'header' => Mage::helper('marketplace')->__('Reason'),
'index' => 'deny',
'type' => 'text',
'filter' => false,
'sortable' => false
));
$this->addExportType('*/*/exportCsv', Mage::helper('marketplace')->__('CSV'));
$this->addExportType('*/*/exportXml', Mage::helper('marketplace')->__('XML'));
return parent::_prepareColumns();
}
public function getRowUrl($row)
{
return $this->getUrl('*/*/edit', array('id'=>$row->getId()));
}
}
I want to rewrite the following class
<?php
class Webkul_Marketplace_Block_Adminhtml_Partners_Grid extends Mage_Adminhtml_Block_Widget_Grid
{
But my changes aren't reflecting in the admin panel. I have searched a lot about this problem but no solution is working.
Thanks in advance.