President Trump touted the effectiveness of newly-constructed barriers as he toured the U.S. -Mexico border near San Diego on Wednesday, insisting, "This wall can't be climbed".
Trump told reporters he expected that almost 500 miles (800 km) of new barrier would be completed by the end of next year.
"You can fry an egg on that wall", e said.
He also suggested he is living up to his promise to make Mexico pay for the wall by pointing to their stepped-up efforts to combat the flow of immigration from Central America.
"When the wall is built, it will be virtually impossible to come over illegally, and then we're able to take border control and put them at points of entry", Trump said. Crowd chants of "Build the Wall!" are often the loudest at his political rallies across the country.
Trump admitted that he envisioned a solid concrete wall when he campaigned for president, but he was told by border officials that they preferred a wall constructed by concrete-filled bollards so they could see through it.
When Trump asked Army Corps Lt. Gen. Todd Semonite to explain how technology embedded in the wall alerts agents to illegal activity, he was told, "Sir, there could be some merit in not discussing it".
He said he could probably pay for the wall through tariffs on Mexico, though he didn't want to impose one just yet.
Democrats sharply criticize Trump's policies and do not believe a wall is the answer to the country's immigration challenges.
Mr. Trump, who declared an emergency to reshuffle funds for his wall, said he still thinks there is a crisis at the southern border.
The president's campaign and the Republican National Committee were expected to raise some $15 million at events during Trump's western trip, according to an RNC official. Ahead of the president's visit, protesters have inflated the "baby Trump" balloon in downtown San Diego.
"I'm here to tell you that's false", he said, telling reporters that Trump reached out to border experts to find out what they needed.
Big-city mayors in California have said the homelessness problem in the most-populous US state should not be a partisan issue.